Proper Neck Tension - How Case Neck Tension Affects Performance

[@devlinautry2702]

I need to give credit to Sam at Panhandle Precision KZbin channel and website. I use .002" neck tension. Redding S series bushing die. Low SD. Annealing my brass before sizing was the key to keeping SD low. Brass work hardens. Like all the hard work and sharing all KZbinrs do. I appreciate your work. I choose facts over feelings. Great work ! Keep the facts coming.

[@carpenoctem5421]

So then by that logic… I’d imagine a good practice to follow would be .003 if it’s NOT hardened brass (as it will have more spring back) and .002 if it’s annealed first. That’s my takeaway here, any thoughts?

[@AgileK9TopDog]

When I use the 306 mandrel I have found that the neck ID is 305 (as measured using the 21st Century mandrels as "pin gauges" and using machinist tube ID gauge). That equals 001 springback. Assuming my measurements are accurate, my actual "neck tension" (interference fit) is 003.

[@wsollers1]

The talking hands remind me of JRB videos :) I run .002" neck tension set by bushing on Hornady match grade die. Been so happy with the results haven't switched or experimented.

[@rustyshackleford2723]

Great routine.

[@PracticallySquared1]

I've been happy with the performance of my redding type s bushings. I just do what they say, .002 smaller then loaded round.

[@chadwickwicky67]

Thanks for the vid! Recently got into expander mandrels, so far for me in .308 , .3065 and .307 is very close in overall performance but still have to do more experimenting. It’s crazy how the learning never ends no matter how much or long one reloads. Just when I think I’m done load developing for one rifle, something comes up that gives the urge to experiment more. Wished I learned about these when I first started years ago. The fun never ends. It’s such a fascinating hobby!

[@hrbricker]

You're on the right track. Hopefully you will develop enough skill before your time and money runs out.

[@WoodrowWoods2007]

Man, this was a great video. This beginner reloader just learned more about neck tension in one video than anywhere else!

[@RichardCasto]

Nice video. This is a deep topic that you probably just scratched the surface. I use a combo of neck bushings (undersize) and then follow up with an expanding mandrel (open back up to my desired amount). My theory is that the neck bushing gets it close, but as you point out, it sizes the external of the case, not the interior of the neck. I then use the mandrel which should size the interior of the neck to be cylindrical plus set the desired size of the interference fit (I am doing .002"). I don't turn necks to try to get a uniform thickness, but it would be interesting to see how that impacts things. As to measuring springback, I think you should be able to use pin gauges (precision ground pins of specific diameters similar to the mandrels) to measure how much if any springback is happening. Then again, it might be very small and hard to measure in a repeatable way because with after annealing the springback might be small? Overall, I am still somewhat new to reloading and don't want to make conclusions as to "what works best" based upon my experience. I just don't think I have done enough scientific testing (as you are trying) to show what some small changes to your workflow might have on accuracy and precision.

[@contactericjones]

My thoughts would be that you developed the load using "0.002 of neck tension". You then used the ideal powder charge and bullet seating depth you found for .002 of neck tension to test the possible effect of "neck tension". However, if you prepped brass with a "neck tension" of .003 it is perfectly conceivable that you might find a better group with an ideal powder charge and bullet seating depth for the .003 of neck tension. Considering the variables involved I think you would need to do load development for each value of neck tension and then compare the best loads from each value of neck tension. That's a lot of testing and conceivably you would shoot out your barrel testing in 6mm. You would then have to rebarrel and redo all the testing, lol.... good thing 308 barrel life is pretty good!

[@cmb7481]

Exactly what Eric said!!!!!!!

[@513Headstrong]

Maybe to fine "the perfect" load, but just testing "neck tension" effects, changing the other variables would nullify the results,

[@RJ-sr5dv]

Fascinating Stuff. Thanks to to the OP and the other contributors. Here is my experience after hundreds of rounds tested Best Results: .003 Neck tension using Redding Bushing die Rifle: Savage 110FP 223 Twist: 1/9 Weighted to 17lbs Trigger: Canjar Set to 2 OZ Front Rest: Bald Eagle Front Stock: Mated to Front rest (rail type set up) Rear rest: Sand bag formed to stock Shooting Free recoil in rest with no human contact with the stock other then the set 2 oz. trigger Scope: 40 Power Barrel Tuner: Type forgotten My Load Development technique: Pick a specific bullet / case / primer / powder.... Stay with it until determined that it is unworkable. Using Audett (sp) ladder to find best charge range Crony for SD and ES Using Redding bushing dies: Adjust neck tension for accuracy {ALL Brass Neck Wall thickness Trimmed to 10/1,000) Brass neck sized only I have not annealed in the past although having read the excellent posts from Rotas and others below I might give that a try. Best average consistent results in this gun; .2s Bullet: Berger 70 Gr LTB Powder: H322 and Vitovori 135 .003 Neck tension using Redding Bushing die Seating depth tested from .005 off the lands to just touching to jamb .005 This is basically a budget bench rest gun. I am not a "good shot" so I had to remove the human component for load development.

[@don_sharon]

I use .001 neck tension with my 6.5cm, 140 gn Berger powered by Varget powder. The rifle is an RPR and avg MOA this weekend on 25 round was .502 (like I can get that precise measuring a hole in paper, but that's the average). No groups were over .550 at 100 yards. These are loaded one at a time only. Fed via magazine and consistency is out the door due to bullet depth changes. I use Lapua brass. I use this neck tension, Varget, Burger bullets, Fed primers, LE Wilson bullet seater and so on, for consistency - except environmental factors, everything I do is consistent from one cartridge to the next. I do not measure run-out. Lastly, I set bullet depth to what is called for in the Hornady reloaders manual for COAL. I don't care about jump, jam or whatever with the consistency I am seeing above.

[@CJ-ty8sv]

Albeit a bit older video but a very good video and the results in the end are *EXACTLY* what I expected (the size that was used for the original development resulted in the best results and I will explain why after a few things to point out first. 1) with regards to what *"neck tension"* actually means from an engineering standpoint which is the hoop stress within the neck of the assembled cartridge, the SAAMI definition is the correct definition of "neck tension". 2) the force measurement to seat the projectile is the best method to gauge what the tension (by definition) is and the consistency from cartridge to cartridge. This is the standard method used in almost all industries where interference / press fits are used like bearing on shafts for example. Bearing manufactures will publish or give out upon request the max fitting force for interference / press fits between a shaft and the bore of a given bearing which is a derived value for the max allowable hoop stress within the inner race of the bearing before it either experiences too much dimensional change on raceway of the the inner race (i.e., making the rolling element too tight) and / or stresses the material too close to its ultimate yield before plastic deformation and or cracking occurs. With regards to bullet seating, obviously we want this to be about as low as possible because of the combustion process. 3) using specific dimensional difference can work well (like saying, a .002" difference / interference) *IF* all other things, especially the amount of anneal / hardness are consistent. Inconsistencies here will lead to inconsistent hoop stress from cartridge to cartridge regardless if the dimensions are the same. A materials tensile strength changes with its state of hardness or anneal (increases with hardening and decreases with softening) and higher tensile strength = more applied load for a given amount of stretch. Think of it like a spring, the higher the tensile strength of the spring, the more force it will take to stretch it say 1" (or think of it as the more resistance it has to being stretched and the same thing is going on with the neck of the case, the high its tensile strength from work hardening, the more it applies a counter force to the stretching force from the projectile being seated so basically the more grip it has on the bullet for the given amount of stretch). And lastly, why the results are exactly what I would have suspected knowing that the .306" expander was what was used during initial load development is because the load development is dependent on this factor. Neck tension is one of the many factors that directly effect combustion rate because it directly effects the initial onset of combustion / pressure rise. Since initially a "good" charge weight was chosen off of a variable that was already given a specific value, changing that value either way will take it out of that "good" zone because the value (really specific tension) was a determining factor for the initial charge chosen. Basically if say .307 expander was used for the initial development, it would be likely that 40.8gn charge would NOT have been the charge that gave the best results and what ever charge that did result in the best, if used here would have shown the best results using the .307 mandrel over the others in this test. From everything I've personally seen / experienced over the years, with consistent annealing, what ever neck tension (neck size) used for initial development will always result in the best to use size because of its effect on the initial onset of combustion. Basically when doing an load development, this is a variable that effects the development BUT you have predetermined a value for this variable and thus arrived at the best results based on this predetermined value so changing the value after will no longer give best results because what was "good" for that specific value is not good for the other specifics. Think of it like temperature stability of powders, even the most stable of powders will have some change with temperature change (just not as much as others) and if you do a load workup at say in the 50°'s, you are going to see a difference if the temp is say 100° it might not be much or all that significant in some cases but the fact remains that the combustion process chances and what was good at one value of a variable (temperature in this case) is not the same as what it is at another value of that variable. All in all, other than seating depth, any variable that is given a predetermined value at the time of load development with regards to combustion itself, that value will be the best value to always use if you can (I say if you can because of the temperature one which we are at the mercy of mother nature with that one). Its the same reason why changes in case volume result in differences in SD, ES and average velocity for a given charge weight.... Consistency is the name of the game, not the specific value for a give variable

[@Jeff_Seely]

This is a very informative video and of great significance to my own resizing practices. I have a Forster bushing bump die with a couple of SAC bushings. My most accurate method is to bump the shoulder ~0.002in and putting 0.002in of tension on my 6.5CM. Those rounds with H4350 yield the smallest groups out of anything I've tried. Those SAC bushings are miracle workers. I bought them after watching your product test and you told no lies. They work very well in my die. Thank you brother!

[@tomvollman3143]

I just started using the 21st Century expander mandrels and I think they are the best way to set neck tension. Like you I don't worry about spring back but I can tell you that a combination of .002 neck tension on my 6.5 CM rounds along with an OACL of 2.800 is producing sub-moa groups at 200 meters out of my Ruger Hawkeye LR target. I think that moving away from the Lands has been as impactful as tuning the neck tension. Having said that I would add that my experience is only valid for my Ruger. My Savage Elite is probably another story. Each rifle has it's own personality. :-)

[@notyou1877]

The purpose of the neck tension is to hold the projectile securely until pressure builds up in the case sufficient enough to ignite entire volume of the powder before the bullet starts to move out. The second purpose of the neck is to seal the combustion gasses and prevent them from leaking backwards toward the bolt head. All that gas volume has to go forward towards the muzzle and stay consistent to reach accuracy.

[@milboltnut]

Not You...... consistent neck tension prevents changes in Standard Deviation, in other words, pressure spikes, and not enough sufficient pressure as you say. Variations in pressure is what causes erratic point of impact.

[@notyou1877]

@@milboltnut isn't that what I just said?

[@Jaygorski]

I use a Sinclair .242" carbide exp mandrel for our 6 creeds, we got more than just a few groups that measure 1.5" for 4 shots with one shot out a bit at 600yds this past season.

[@RJ-sr5dv]

Wow! 1.5” at 600 yards

[@randybrown2623]

After using the -.002 mandrel on my 6.5 CM the first 10 groups of 5 rounds each were all single digit SD, despite a .3 gr incremental difference in the charge weight. I have been using Redding bushing neck sizing dies for a long while with .002 under bullet diameter and had not gotten as consistently low sd before using the expander mandrel. I anneal each cycle so the expander had a definite positive influence. Seating with a Hydro Press by 21st Century and LE Wilson inline die showed 40psi seating pressure consistently. No doubt, the expander mandrel removes variability of neck tension. Great info. Thanks for the videos

[@BoltActionReloading]

Glad they help!

[@cademarti1365]

@@BoltActionReloading so are you fl resizing with a regular old expander ball then running a mandrel through them or are you using a bushing die?

[@BoltActionReloading]

For my standard process (at the moment) I remove the factory expander completely, FL size with a .002" bump, and then go back with a Mandel. 002" under projectile diameter.

[@cademarti1365]

Using a bushing die at all to squeeze the neck in?

[@BoltActionReloading]

Not a bushing die. A regular FL die.

[@lucasrose8272]

Been running bushing dies for many years with great results started using the Sinclair expander mandrel this year and it had made a difference in concentricity which improved groups sizes. I have with great luck used two thousands neck tension in many types of loads seem to work well.

[@chipsterb4946]

When you say “2 thousandths”, do you mean a mandrel .002” smaller in diameter than the measured bullet diameter, or do you mean that you make the outside neck diameter 2 thousandths smaller than a loaded cartridge? I assume the first but ….

[@bryanmarks4070]

I used to use a match Hornady die for my 6.5cm. When I was seating bullets I noticed some were easy and some were hard. I switched to a basic Hornady FL die with the stem and expander taken out. Then I run them thru a expander that’s 2thou under bullet diameter. Now bullet seating is all the same and my SD/ES are lower.

[@jacob04103]

I have the same set. They do not come with kneck sizing bushings. You need to pick the size you want and order it separately.

[@GB-zi6qr]

Wow! So novice reloader here. I'm learning with .223 Rem. Through my rifle, using 21.4grns of H335 under a Hornady 62grn BTHP, with a COAL of about 2.250 I'm regularly printing sub 1" groups. I'm using the Lee 4 die set, I forget which model. Just took measurements, if I did this right, I'm getting about 0.005" of interference fit depending on brass. I shoot a lot of range pick up brass. Pretty happy any way because I never thought I'd be able to shoot sub 1" groups.

[@Gnolomweb]

If I sort range brass by: head stamp, weight and volume... I get the same groups as my Laupa new brass.

[@Jeff_Seely]

I am thankful for this comprehensive study. Some believe that uniform neck tension has little impact on accuracy. I believe that it significantly does, and you proved it with this. I will be buying a similar range of mandrels that you did but for a .265in bullet. I would think that uniform neck tension impacts smaller diameter pills more than larger ones. This sport is a game of eliminating as many variables as possible and I think that for the money, this expander is a good investment.

[@mostachiocam1598]

Am I the only one who watches your videos at .75 playback speed. So much info! Thank you

[@cmb7481]

Exactly what Eric said!!!!!! In short to changing one parameter will have an impact on the others which can then be adjusted to return to our base line. Thanks for sharing.

[@warpedweirdo]

Thanks for the data man. I appreciate the effort it took to provide this info.

[@impactaustria]

I'm using Reddings Type S FL die (without bushing) and Competition shellholders to FL size and set back the shoulders about .002" and a polished Lee (!) collet neck sizer, giving me between .0015" and .002" neck tension in my .308. I don't like the extra step that much but it has given me slightly better results (SD/ES and concentricity). Also the Neck ID of my howa factory barrel is likely larger than on most custom barrels, so sizing the neck radially seems a bit gentler than axially pushing it through a bushing.

[@BurnDuration]

Awesome video, and very clear and well organized material! Very interesting results. I recall Mark and Sam after work did a case crimping test on .22 WMR, and found velocity to increase with crimp. I think neck tension and crimp influences the time at which the bullet engages the rifling, as higher tension would release bullet from the case mouth at a later point during the pressure curve. As work = force x distance, in the .22 WMR test, the bullet was acted upon by a greater force as the muzzle velocities were higher with the higher crimp case. On my Lee .308 FL sizing dies, I’ve noticed it sizes to 0.306” case mouth, and on my RBCS .308 FL sizing dies it sizes slightly tighter to 0.305” case mouth on federal brass. When I’m seating 168 gr SMKs, I really can’t tell any difference in seating pressure by hand. In both sets of dies, I’ve shot 0.3 to 0.5 MOA groups with 42.4 grains of IMR 4064, seating at 2.200” CBTO. It would be interesting to see a crimp variation test as well. (I personally don’t crimp, as I’ve found the 0.002-0.003” neck tension to be sufficient.)

[@p1choco]

I forget who's channel, I watched, but according to this F class shooter, the dwell time when using an expander mandrel also has an effect on the cases spring back rate. Minimum time was 4 or 7 seconds to hold the brass in the mandrel. I can't remember exactly.

[@Sanman1]

Quite true. Run your case up, leave it there for 5 seconds, then retract...

[@hankbrinlee4677]

Believe that was F-Class John, another excellent KZbin channel...

[@brucebrill3248]

I do the same with a bushing -just let the neck sit in there for a few second, and let it spread the brass around a little bit? Who the heck knows...

[@wilburnmartin9522]

I will let mine sit in the FL die for several seconds when I get one that is tougher to size for spring back. Also for changing x to y caliber like 7x57 to 257-roberts. Most of my brass have been range pick ups or purchased "once" fired from other reloaders.

[@samuelcarstens6152]

This video comes to mind. Bonds stretching and atoms finding new neighbors. kzbin.info/www/bejne/pni6hItspbinmpI

[@mab0852]

AMU .003 is taking into account spring back from the bushing to land on .002 finished neck tension. In your case, measure neck diameter and thickness post bushing to determine the presized ID. Then run the the mandrel through and recheck the OD and thickness to get the ID. The difference from the mandrel is the spring back for that given amount of neck sizing. Or you could just use your small mandrels as check pins and measure it directly. It's really not going to vary significantly over that small of a size range if everything is consistently annealed.

[@hankbrinlee4677]

Lots of food for thought right here... excellent vid!

[@greggavin5078]

Ll

[@hawkeyeammosmithing]

I’ve found .002” of tension has worked the best for me as well. I currently use the TiN coated “turning” mandrels from Sinclair, along with their mandrel body, for that task. I use a Forster Bump sizing die to size my brass in a first step, then the mandrel setup in a second step. The bump die uses a bushing to size the neck, and it will also bump the shoulders. There is no expander. I use this die with the applicable sized bushing to bump my shoulders back .002” and so I don’t overwork the necks any more than necessary before using the mandrel to set the final tension, unlike a gutted full length sizing die would do. I have used gutted FL sizing dies in the past, and I can’t say I’ve actually had any issues by using them versus the bump die I use now, but I still at least feel better using a bushing that works the brass a bit less. Anyway, so I decap and wash my brass first, and then anneal it, then I lube and size my brass with that bump die, then remove the lube in a dry tumbler. I then dip the cases in graphite before running the brass through that mandrel setup. I leave the graphite on the cases since it won’t negatively effect anything and will actually increase consistency with the amount of force required to seat bullets. This method has proven to work extremely well and produce very consistent and reliable ammo. I haven’t noticed you use or talk about the Forster Bump Dies, and if you haven’t tried them, I highly suggest trying one.

[@hewlett260]

I've found .002" to be the best for my rifles across three different calibers and 5 barrels. I run full length bushing dies and bump the shoulders .002 as well. All of my rifles have been 1/2 moa or better with great ES/SD since moving over to bushing dies.

[@chipsterb4946]

This is a fantastically educational video. At 2:35 I think you meant to say that the full length sizing die UNDERsizes the case neck and then the expander ball is pull back out of the neck, expanding the inside diameter of the neck.

[@rutrose2000]

This video shows up in my feed the same day I buy a Sinclair carbide mandrel for my 6mm. Nice.

[@stefanschug5490]

Nice work! .002" works best for me with mandrel however if you ever checked the variation of bullet weights in the same box of top manufacturers you'll see a reason for flyers and other oddities. There is a good reason why some benchresters make their own cup and core bullets. Sorting the bullets of the same boxes by weight helped my groups to shrink! Keep up the good work !

[@richrudley2650]

I expand my necks just before I put the powder in the case then seat the bullet. But always put graphite in the neck before expanding the neck.

[@jessewerner4067]

Expander mandrel size doesn't determine my neck tension as in your case, feel does. I use whatever size mandrel (pin gauge) I need to in order to get a desired pin gauge size to slide in the case neck with very light resistance. In my case, I sized some 30 Nosler necks a few days ago with a .3075 pin gauge in order to get a very light drag with a .306 pin gauge slipped in the neck by hand. This gives exactly .002" neck tension. Doing it this way also allows extremely consistent neck tension up to the point of any inconsistencies in neck spring back. I think overall, consistent tension case to case is more important than a neck tension number.

[@williambrown8683]

Like you, I have been using the expander mandrels for about the last 4 months. I have been setting my tension by expanding the necks until the bullet will no longer move when pressed against the edge of my bench. Just enough tension to hold the round in place. Lately, I think I should use the next .0005 smaller mandrel? Your thoughts? Great info on your channel!

[@edwardlance2379]

The goal, of course, is consistency. In order to achieve consistency, all factors of the operation have to result in like parameters. Sizing mandrels are only one part of that equation. The spring back of the brass is every bit as important, but is the one parameter we don't have a great deal of control over. One possible solution is to use quality brass, all the same brand and batch, sized, trimmed, and fully prepped. Then, a proper annealing, preferably on a quality annealing device. This will help ensure the properties of the neck are as equal as we can make them from the spring back perspective. Additional steps could include sorting cases by weight and capacity, concentricity, and neck turning (inside and outside) to achieve a batch of brass that is as equal to each other in every possible parameter you can measure or affect with tooling or processing. Bullets can be sorted by weight and diameter as well. The bottom line is consistency is a trade off of time and effort, at least within the confines of what we can do to make cartridges consistent with each other.

[@gorillamotors]

Absolutely GREAT info. I too use expander mandrels for the 6 ARC and 6.5 Creedmoor. I seems that my Bergers like 0.002 the best.

[@fernandochavez7807]

The testing you do brings a lot of clarity to issues that arise during load development! Thanks for sharing.

[@mholman9711]

Outstanding, thank you.. Me I focus on neck Consistency by sorting with a Redding neck checker, I also do a single treatment from the lee collet neck die all Sorted into 3 piles of brass, good, fixed and garbage. I full length size everything always ... Apples and oranges, But I did do experiments with *HOT* 45 Colt loads using 2400 powder a half dozen dies sets, maxed neck tension and a solid crimp made a huge difference .. Take care

[@mightyarmoryprecision]

Powder charge and bullet seating depth play a big roll in muzzle velocity and accuracy. So many factors which brings us to load development and that’s for a specific rifle. This is all part of the loading experience. Enjoy and start stacking em’ Video was well done, thank you.

[@Saintsfan1977]

Not accuracy. 6 thousands of a difference in bullet seating has no effect on accuracy, neither does 0.1gr or 0.5 gr of powder.

[@josiemartin6022]

Great vid, love to hear more on expander mandrel.. just looking at using one myself..

[@johnshepherd7958]

I assume here that all the cases are fully trimmed to the same overall length and flash holes plus primer pockets are reamed to same sizes for consistency. Also all cases are weighed and sorted into same weight groups for tests as the case volume will be proportional to case weight, and case volume alters the energy for a consistent fixed weight of propellant.

[@RealHank1791]

He said right up front he used Lapua Brass, once fired, annealed and trimmed. The rest is irrelevant for Lapua brass. Watch and appreciate the information and stop trying to prove what "you know". It's undoubtedly not much.

[@jerryrochelle3112]

With the numbers , I would’ve like to see the actual seating pressures using force pac or preferably century 21 hydra seater

[@StarSwarm.]

It’s not the neck tension so much as it is the consistency of neck tension between all your cartridges that will affect the accuracy.

[@TexasTrained]

I'd say it's both. Consistency is in any reloading

[@jeffhuntley2921]

Never gave it that much thought. Was told .002 tho was ideal and haven’t had any reason to doubt it. Thanks for the food for thought 👍

[@Slipprymongoose]

See if this wasn’t cartridge reloading I wouldn’t call this neck tension I’d call it the interference fit. Tension denotes a force measurement not a dimensional measurement. Small details that in the grand scheme doesn’t matter much it’s now part of the vernacular.

[@johnshepherd7958]

Correct.

[@SurmaSampo]

Interestingly enough the SAAMI description is the correct description for neck tension. The other descriptions you provide describe the measurement of processes you perform to achieve the described tension. It is like calling the amount of time spent boiling oats porridge i.e. I recommend 45 minutes of porridge for steel cut oats.

[@nycreloader]

Just got around to watching this video. Very good information. Thanks for your hard work. It really describes what is normally an enigma wrapped in a mystery with a bunch of opinions and conjecture. Well done!

[@BoltActionReloading]

Thanks!

[@brucebrill3248]

Don't ya just love this stuff...it made me check my Redding carbide button for 6.5-- yup -.002. The bullet gods have whispered again.

[@Sanman1]

Thanks for the video, and well done. I load a bunch of .308 for myself and friends, and have really great luck in one rifle (.3 MOA and an SD of 7.7) using a .3070" expander mandrel AND I lightly taper crimp after seating. I'm a big fan of taper crimping...

[@rgibson759]

Great job. Could try and standardise things forever, but i think you did a great job of showing the effects of neck tension wrt a baseline load.

[@martingagnon4547]

100% it comfirms your load was optimal already. 100% neck tension affects performance. But, we cannot confirm mandrell 0.306'' is the optimal ID for 0.308'' bullet as a rule of tumb... it is optimal for your particular load that you developed. Nonetheless a very interessting topic and experiment that you did! Data driven video is what I like! Thank you sir.

[@disfunctionjunction8921]

I am researching this because I found my rounds in the magazine of my 300 WBY ( Ultra light Backcountry model) are experiencing a longer AOL after a round is fired. I concluded that recoil is seating the ronds deeper in the mag. I had .002. MY smaller calibers no problem.

[@MaxairEngineering]

I agree right with your definition of neck tension. Strictly speaking it is a measurement of force. It is not a dimensional differential measurement. Having said that I realize that in the vernacular this the chosen definition. However the measurement of force to move the projectile “through” the brass neck is determined by the dimensional differential combined with the hardness of the brass and the condition of the surface i.e carbon, roughness, lube etc.

[@prcc]

Amazing! So nice to see real data on this topic.

[@Dv087]

I can really appreciate this You can get away with less neck tension on a bolt gun then you can with an AR-10. You do not want the bullets to start to move in the magazine from recoil or when around is jammed into the chamber. That brings up a different but also important question. Are you better off having more neck tension or crimping the case?

[@ynotjf]

I can’t wrap my head around neck tension. It only requires small pressure differences to overcome neck tension but when the bullet meets the lands it requires a HUGE pressure spike to push the bullet forward forming the land groves into the bullet. I use .015” off the lands so neck tension is only relevant for .015” of the neck travel then that huge pressure spike occurs. How can such small variations in the pressure curve have any effect on accuracy when compared against the enormous force required to push the bullet down the barrel, yet it does!

[@rotasaustralis]

This type of thinking is where everyone comes undone. You ask how the enormous pressure differences can possibly be connected then, state unequivocally " YET IT DOES". I don't think they're connected at all the way that most think.

[@mab0852]

It seems insignificant. But its a timing thing. The neck fully opens before the bullet moves that .015 so some of the gas blows by and down the barrel before the bullet seals the barrel end of chamber. If that released volume isn't consistent round to round then you have a pressure and speed differential. There's a natural sweet spot where everything times just right and variation settles down giving the low ES and SD numbers like in the graph. Years of history has shown .002 in bolt guns and .004 in semiautos is the best place to be. Some of the benchrest guys use almost no neck tension, but they're single feeding and their brass and chambers are so closely matched they can get away with that.

[@rotasaustralis]

@@mab0852 I can't really see your explanation as the reason for low SD numbers. Now I certainly can't disprove what you say but, if this were the mechanism, I can't help but think that a barrel with a worn throat should create an excellent situation whereby the bullet would completely seal the barrel every time. Also, I don't know about the neck opening before the bullet moves. I'm not sure how that mechanism would operate.

[@mab0852]

@@rotasaustralis It's about total gas volume not the pressure. The pressure curve and available volume of gas to propel a bullet down the barrel are two different things. You can generate a huge pressure curve that will break the action but not produce enough expansion to push the bullet down the barrel. Pressure curve is highly affected by seating depth. That's why running a max charge and having the bullet in the lands is very dangerous. The dynamics of the detonating charge blow out the case to fit the chamber almost instantly. As the powder charge ignites from back to front the neck is the last thing to open and it's more or less holding the bullet until the neck completely expands releasing it to travel forward. Just like how a long skinny balloon blows up...tip inflates last. The gas already has velocity at that point and goes by the bullet as it begins to accelerate toward the lands. That hot escaping gas is basically flame cutting like a torch as it goes around the bullet (significant factor in throat erosion). That's why short fat cases burn barrels quicker than longer skinnier cases. That's also why powder burn rate is so important. There has to be a balanced relationship in pressure, the volume of gas and its rate of expansion, that push the bullet down the barrel. Not enough, squib...too much to fast and and the gun blows, not the bullet. Not a good idea, but a round detonated outside the chamber won't send a bullet very far if at all before the case splits. I'm sure there is some hi speed video out there that shows all that in action.

[@rotasaustralis]

@@mab0852 Yes, from what I've read the powder charge must be balanced as you've stated however, I've never been convinced as to the validity of the bullet seating depth as a factor which affects burn rate, at least not directly. At the moment, I am leaning toward seating depth creating a timing mechanism but, more to do with the barrel vibration frequency. The presently understood internal ballistics mechanism starts with the bullet being pushed forward into the lands by the primer ignition where, there is a microsecond delay then, the main body of the charge burns & etc. This is the initial mechanism that I believe is directly affected by the neck tension. When the bullet is pushed fwd into the lands, a larger powder chamber is created which sets conditions for the burn rate of the main charge. I believe at the moment that, the much lower pressure pulse of the primer pushing on the powder column is affected by neck tension. If we consider all the anecdotal associations of low neck tension resulting in lower SD's, I think there is a definite correlation. I think neck tension sets the conditions which govern how far the bullet is pushed up the barrel which in turn, sets the length of the newly formed powder chamber. The less neck tension, the lower that initial primer burn pressure , reducing the bullet jam variation & minimizing the length of the burn chamber. Since the primer compound is much faster in burn rate, I believe it either builds significantly more pressure or, ignites more of the main charge at the base if the neck tension is high, resulting in higher initial pressure which, bangs the bullet further into the barrel before the main powder column conflagrates.

[@Dwayne7834]

Thanks for sharing your information and videos. I always enjoy and appreciate videos. I have 308 dies in Lee and Hornady. When resizing I end up with a neck measurement of .304 - 305 . Neck tension has been the hardest thing for me to fully understand. Maybe I am little hard headed. LOL

[@chuckfinley3152]

The Lee collet die just works, you can order different mandrels to change neck tension too, I find that my brass lasts forever unless I crank the loads up enough to stretch the primmer pockets out, if it gets fussy I'll bump it with a Redding body die or fl die, guns not picky but I do better groups and statistics with the collet die, ymmv

[@Propelled]

I too am a fan of this die. It actually eliminates most of what this poster is speaking of as variants, even makes thickness consistent. Wet tumble, trim to length, push bulge in front of the belt on my magnums, trim to length, dress primer pockets and flash holes, Lee collet neck die, prime, charge, load, soft crimp with the collet crimp. Dead even bullet tension, perfect concentricity. On my .308 AR ammo, I had Forster open up the neck on their full length die to leave it alone, bump back the shoulder .003”, - wet tumble, full length, trim, primer pocket/flash hole, collet neck size, prime, charge, load, collet crimp. Perfectly concentric ammo, perfectly consistent neck tension IN FULL LENGTH SIZED BRASS! (And it does make a difference!)

[@TexasTrained]

I think unless you check each brass wall thickness you are still just guessing .I don't know if that would even affect my shooting. Great video

[@Charles-xw2wy]

there was another video about bullet settling during travel .. not sure the affect it has .. but was demonstratable.

[@lencac7952]

Hi Bolt: I love this kind of chit. Anyway, I'll have to get the expander mandrels now ........ thanks (-; Hey, here's something to think about. Optimum flash hole size and case neck length vs the chamber neck length. And is the face of the neck on the case cut exactly perpendicular to the axis of the bore? What's the distance between the lands and the case neck. Then you got the bullet seating depth vs the lands clearance, case volume, bullet weights. The incarnations are endless. Note that there is a moment that the bullet is little more than a piston in a cylinder while it is supported by both bore and case. The case is molten at that moment and I believe that's where the bullet can become misaligned to the bore causing the bullet to corkscrew. It's centerline is correct but it shows up on the target as a slight spread. BR shooters would say the bullet hasn't gone to sleep.

[@raymondmichael3077]

I swab the inside of the case neck with Hornady One Shot liquid, to hopefully reduce stress on brass shoulder and get more consistant next tension.

[@additudeobx]

Of course when we are using a bolt gun and sliding that cartridge into the breech with consideration a .002 "neck" is tolerable, but what about on an semi-auto AR platform where the cartridge is essentially driven into the breach with much more force? If the bullet is not tightly tensioned in the case mouth the bullet could effectively slide forward lessoning bullet seating depth. Or is .002 enough neck tension to avoid that possibility in an AR?

[@RJ-sr5dv]

All bets are off in the (sloppy) AR platform With a very short neck (556) concentricity is questionable. ARs in my opinion are minute of bad guy and not MOA

[@cjtathome]

The name of the channel is Bolt action reloading

[@tadbarker7082]

Excellent info. I like mandrel idea for consistency.

[@johnshepherd7958]

Brass spring back will vary dependant on how many reloads per case due to the neck brass work hardening, plus if annealed or not.

[@hrbricker]

Sounds simple enough to me. I want to know just how much force is required to separate the seated bullet from the cartridge case at ignition. This will influence the amount of pressure developed before the bullet moves at all and thus the initial acceleration rate. Along with charge, headspace, jump and barrel friction, neck tension affects the position of the bullet relative to barrel resonance at the instant of exit from the muzzle. Simple right? It's kind of like calling the wind accurately except that we can measure neck tension by its effect on group size.

[@Russell-1]

Do you think you had enough samples (i.e. fired enough groups) to come to any reliable & repeatable conclusion?

[@lencac7952]

Hi Bolt: I love this kind of chit. Anyway, I'll have to get the expander mandrels now ........ thanks (-; Hey, here's something to think about. Optimum flash hole size and case neck length vs the chamber neck length. And is the face of the neck on the case cut exactly perpendicular to the axis of the bore? What's the distance between the lands and the case neck. Then you got the bullet seating depth vs the lands clearance. The incarnations are endless. And the shelves are bare.

[@sjohnson1776]

Good stuff and thanks! I run .002 " tension on my 6.5C and .015" on the .223. Both consistently shoot sub 1/2 MOA. That said, I'm not impressed with the statistical results I get. Runout on the sized brass and final loaded round is very low (as in the needle barely moves at all)I feel like my ES and SD's should be single digits and I've never achieved it. I use Redding competition bushing dies FYI. I also use a Forster inside neck reamer on fired brass. The brass is Gunwerks for the 6.5 and currently Sig for the .223. I'm waiting on some starline brass now for the .223 so I'll be interested to see 1:1 comparison vs what I currently have. Thanks again!

[@fentonpainter7907]

I think you mean .0015” don’t you?

[@sjohnson1776]

@@fentonpainter7907 yes! THX!

[@coloradodrew]

Are you annealing?

[@sjohnson1776]

@@coloradodrew Yes I am.

[@milboltnut]

expander mandrel sized case neck outside diameter, verses seated bullet outside neck diameter. My .30 caliber loads, are, .328 sized case neck OD, seated bullet is neck OD .329. Expander Mandrel .307 Under 1/2 inch MOA, almost 3 shot one hole group. It's alot cheaper using mandrels than bushings to neck size.

[@JohnSmith-ir5pv]

I use .003 neck bushing under loaded od with a .307 mandrel for my .308 only getting .001 neck tension is what works for me... my thinking is the least amount of resistance the bullet has being held in the case the less it is slowed down/ friction leaving the brass.. minute but works

[@ytmachx]

First I turn the necks to achieve a consistent neck thickness then resize with a bump die with bushing for .002 tension

[@johnhutcheson8869]

What about using a Lee Factory Crimp Die on large bore to insure recoil doesn't adversely affect rounds in the magazine when chambered round is fired? How do you use the crimo die and what tension is commonly used/wanted for dangerous game?

[@mtnshooter2487]

Depends on what im reloading for. I use a lot or neck tension for the M1A i load for (.003 less then 308,) due to the bolt slaming the round fwd on loading. Compared to very little .001 to a bolt gun.

[@jimlerum]

Good stuff. Great data collection for reloaders.

[@gwidwock]

I don't know how to explain this any other way but eight minutes into this video my f**king head exploded. 🤠

[@patrickscheel3943]

Another amazing video! Have you looked into comparing the Lee Neck Sizing Collet die to the mandrel neck sizing with regard to extreme spread/SD/group size comparison? If looking at concentricity be sure to check it at the tip of the bullet rather than the brass neck as the collet die forces irregularities in the brass to the outside. It's extremely cheap ($35) and if set up properly on a press and given a 3 second hold, a quarter turn and another 3 second hold it has the most consistent velocities I've seen (and I don't have to turn necks 😏) Keep up the great work!!

[@luiscolon921]

That's a good question. I previously reached out to Lee about it. For my application, Ar-15 300 BLK, I needed to resize first then at times use a custom sized mandrel to "expand" the neck for the instances where I was loading a bullet larger than .308. Lee told me the collet die was designed to size "down" to a particular dimension and not "expand" a neck on a resized case. I understand this wouldn't be an issue for those that don't full length resize.

[@chriscockerham7856]

Geezus that’s deep. Good stuff

[@stiffdrinkmime366]

I am a newbie to reloading, but arent we talking about like 60,000 psi of case pressure? Does a pound or two of friction really make a measurable difference? Thank you for doing all of the work required here!

[@martingagnon4547]

That little pound or 2 of variation friction actually equates of how many combustion gases leak there will be prior to get full seal of the chamber by the bullet in the barrel. So low variation in neck tension equals low variation in gases leak equals low SD.

[@jeremys8360]

When does this all matter? If I get good accuracy, do I need to change? I’m using regular old rcbs full length sizing dies, 1993 Remington 700 in 308 win, and .3-.5 moa

[@p1choco]

It all matters when shooting long range. Just because you're getting small groups at 100 yards with a 308 doesn't mean much. I get .75 with a 30-30 at 100. Honestly with a good tuned load, you could have that 308 punching one ragged hole at 100. So depending on your intended purpose, good enough to you is all up to you.

[@freeandcriticalthinker4431]

It’s Matters big time when your trying to ring the bell at 2500 yards

[@trg3761]

I use to think all bushing where all the same, how wrong i was. iv been using a 337 redding bushing on my lapua 308w brass for 10 years. A month ago i bought a forster neck tension gauge and checked the neck tension on my redding 337 annealed once fired lapua brass. To my surprise the gauge would not even enter the case on the smallest 304 size. so i decided to get a few Whidden bushing started with 338 337 336. the 337 gave me a close fit on the 336 pin. 336 gave me a tight fit on a 336 pin. Next i will be getting a few expander mandrels to try.

[@ArmenArmenjs]

Great video!What is the process to figure out the mandrel size for final tension. meaning for 6.5cm. My loaded bullet neck size is .294, I don't use neck bushing just FL die. I like say .002 neck tension what is the mandrel size for 21st Century is adequate. process for arriving to the result. Thanks so much for your videos, this hobby is like chasing rabbit it never ends.

[@rotasaustralis]

In order to clarify my previous comment, I think it important to understand exactly what your method is testing. Your method seems to me to be valid for testing stepped, general neck tension reduction but, not neck tension consistency. Ofcourse, if the overall neck tension is reduced then, so also is the relative magnitude of the absolute neck tension variation as a ratio. So, neck tension variation will reduce as an absolute value but, only by default & not design. This is not to suggest that the results are not meaningful as, I believe they are or, can be however, it is important to be clear on the distinction between reducing average neck tension & not consistency. In this case, I am confident that, in general, the consistency will indeed improve driven by the physical properties of the brass but, not necessarily & certainly not as a determinative function.

[@brendavanorden9550]

Did you use a seating pressure gauge? If so it would be helpful to know if you sorted the loads according to seating pressure. Not just the assuming they will all spring back the same. You extreme spread and groups should be better if you use the seating pressure instead . I would like to see a vid where you use the same mandrel and grouped your bullets by the seating pressure . Say 10 shot groups.

[@raulmartinez7730]

Best explained imposible!

[@legallimitoutdoors9917]

Can I use the 212gr PRC in my 300WM cartridge for reloading And will they fit. Thanks for the show's I'm learning so much thanks 🇺🇸 2A 🇺🇸

[@mybuickskill6979]

Im curious to see more. Like would it be powder dependant? Probably bullet dependant. Like different stuff might like different tensions. Or is it more of a rifle oriented thing.

[@frankrubeshaw4673]

Hi great video. Do you know what the empty case neck measures before sizing, after sizing and after mandrel are? Just wondering how much the case moves each time. Thanks

[@phils5411]

I use .002 neck tension with Redding bushing match grade.

[@toddb930]

What do you use to lube the inside of the necks before inserting the expander mandrel?

[@kihara4244]

I use a bushing to resize to 0.003" and then run a mandrel to 0.002" - not overworking the brass and works for me....

[@spencerhurley8359]

So you run it through a Full Length Bushing Die and then run it over a mandrel as a second step? Or you use the mandrel in the die?

[@kihara4244]

@@spencerhurley8359 seperate steps

[@spencerhurley8359]

@@kihara4244 so no expander ball when you run it through the die?

[@kihara4244]

@@spencerhurley8359 nope, i take it out. Massive improvememt in consistency

[@spencerhurley8359]

@@kihara4244 I've been having muzzle velocity problems and I found out my neck tension was .001" way too light... trying to find a new way to set it so thanks

[@ronaldyeater3322]

For neck tention I have been useing 4 turret press. When I use lanolin and 99% alcohol I start at full length case sizing and run through all dies. I assume very little lube will be left seating and crimping. Always thought that helps? Am I wrong?

[@shaneb704]

How far did you neck down the brass before using the expander mandrel

[@j-sincopeytargetsmasher3781]

Ok maybe I’m lost… but what does changing the neck size of you run it over a a standard mandrel? Should you maybe use the neck bushing after with out the mandrel ?

[@RealHank1791]

Excellent video and information sir. Thank you.

[@BoltActionReloading]

Thanks hank, I am glad you enjoyed it.

[@daviddiebold7357]

For my hunt load. 2 thousandth with the crimp die squeezing the smallest measure amount I can get -.001 from the outside. Say necks .315 I make the lip .314 taper or lee factory. I have not tested enough to claim anything but was passed down father to son.

[@whliving]

I greatly appreciated this type of experiment. Have you attempted to accurize any of the other neck tensions to see if you were able to reduce group size? - especially the 1.516 group and maybe one of the others that had a tighter es/sd but produced a larger group. Thanks again for the video.

[@conunpocodefe]

Exactly what I thought.

[@SniperC175]

I don't think mandrel size equates to the amount of neck tension. In my experience with mandrels and expanders there is from .0005 - .001 spring back after the mandrel or expander is used. I have also found that the manufacturer of brass (differing metallurgy) and thickness of brass also play a role in how much spring back occurs. Just some more food for thought.

[@dahut3614]

You could actually measure the spring--back by testing with the smaller mandrels after sizing with a larger one. I also wondered if the tension remained the same if you installed the bullet hours, days, or weeks before. But at this point, we're probably chasing a rabbit down a hole!