Smyth Busters: Can You Mix & Match Bolt-Carrier Groups?

One of the great things about the AR-15 platform is its interchangeability of parts. This includes the ease of swapping a different bolt-carrier group into your rifle, which takes all of about 20 seconds. But some folks out on the Internet say, "Don't mix and match AR-15 bolt-carrier groups!" Why not? Let's ask Steve and Caleb.... who say AR-15s are all manufactured to the same specs, so a new bolt-carrier is almost certain to fit in your rifle. Just whip out the headspace gauges and check the headspace on the new BCG. You don't even need a full set of headspace gauges. Just a NO-GO gauge is fine. (Don't use a "field" gauge: that's for military and law enforcement users who put a very large number of rounds through their rifles during training.)
Here's another warning about mixing and matching bolt-carrier groups: Let's say you have two BCGs that both headspace correctly in your rifle. You set one of them aside and shoot thousands of rounds with the other. Don't just swap the "spare" BCG into the gun without checking the headspace again. The lug recesses in the barrel extension have worn while you were shooting with the other BCG, and the spare bolt-carrier group may no longer headspace correctly. How many rounds lead to significant wear? That varies by rifle, type of ammo, gas system pressure, and a lot of other factors. Suffice it to say, the average casual shooter is probably not going to significantly wear the headspace on their rifle any time soon.
So the myth is BUSTED, with a stipulation. You CAN change your AR-15's bolt-carrier group IF you check the headspace when you do it.

[@CalebSavant]

Just because you can say "I did it and nothing bad happened" doesn't mean you should keep doing it. We all know this guy right? Oh, and I said I would timestamp it! 4:27, Steve said check it!

[@falconcowboy9995]

🤣😂😂🤣😅😅😆😆

[@whatsmolly5741]

Ok ok. Thats a fair point but on the other side too many people lack the ability to reason stuff out themselves and just want to be told what to do, which wouldn't be all that bad except modern liability requires me to treat you as if you are the dumbest person who currently walks on this earth, because it's alot easier to say "don't put smokeless powder in hour black powder gun" than to explain that this isn't necessarily true as you can use smokeless powder in a black powder gun but differences in definition of grain and smokeless being 3-4x more powerful you absolutely need to be sure you converted it correctly. Or you know "don't make your own baby powder" not because you can't make baby powder at home but because we're scared you're so stupid you'll kill your baby doing it. If you don't know why you're following a rule that's a problem all in itself.

[@KJ4RMZ]

How about a video on using gauges?

[@whatsmolly5741]

@@DaedalusHelios almost didn't believe you but looks like Brownell is actually out of 223 case gages. Fortunately there is an easy alternative or probably multiple alternatives but ebay is where I got all of case gages and price is virtually the same.

[@chuckb3489]

You guys should do a video on mismatching bolts for the bolt carrier.

[@britjohnson1990]

Its still incredible to me that almost any new bolt and any new barrel will headspace just fine.I dont know anyone who really have had any headspacing problems with any half decent company's products. Its no wonder why its such a popular design. You could never do that with any design that locks up in the receiver. Modern machining and tooling is incredible. I dont see this platform being replaced for 50 years

[@douglass69]

You need to show the gauges and explain exactly what you’re talking about for us that don’t know.

[@virtuaguyverify]

Smyth Busters, not GunSmythers

[@Big0veralls]

For real. I was so lost watching this. I just watched in the hopes that I’ll understand what they were taking about somewhere down the line.

[@blkft]

Go watch SOTAR: School Of The American Rifle His physicals and Autopsies are quite informative.

[@t.lledsmar6052]

They come with detailed instructions

[@CrashRacknShoot]

​@@Big0verallsif not shoot gun lots, don't worry. If shoot gun lots, maaaaaaybe problem. It's simple.

[@jerroldkazynski5480]

The Army had a series of cartoon-ish publications giving hands-on experience tech talks for the care and feeding of M-16s. Wish I had kept them.

[@richardflora7940]

They were called p.m. magazine .

[@dr.froghopper6711]

I learned from those and I was Navy!

[@tomfrommichigan]

You must be referring to the comic book. When I was in the Army in the early '80s, I saw a few of those floating around. I understand that they are collectable now.

[@johnf8877]

Not politically correct. A cartoon of a woman with big breasts telling you to lube your M151a1 would get somebody fired.

[@christinepearson5788]

Sweet 16, reprints are available from Amazon as well as other sources. PM (Preventive Matinence) was the illustrated magazine that contained the "Maggie" character but she was never as shapely as when drawn by Will Insner (yes the Disney guy)

[@2ndchance632]

Interesting. I’ve been ruining two different BCG’s in my AR-15 for years. One is from Aero Precision and the other is from BCM. Checked both with go/no go gauges. Never had an issue with either one. Round count in thousands for both. As always, keep the myth busters coming. I really enjoy watching them. 👍🏻👍🏻

[@truck57us]

I hate it when I ruin a BCG, let alone two of them :) Good to know on your heavily used ones. Agreed on good/fun myth busters.

[@kayakdan48]

Did you mean to say "ruining" or "running"?

[@KendrasEdge757]

I think the main issues occur when you’ve used a well used barrel and swap the BCG with a different well used BCG. Typically if you put a new bolt in on a used barrel you’ll be ok because the average person will never shoot out an AR barrel or BCG.

[@danielczech30]

Many years ago, I was qualifying on the range with an M16A2. I had 2 lugs sheer off of my bolt. I had the range armorer grab the bolt from the weapon of a Marine being dropped from the range at the same time. I ran it without issue.

[@jonathansmith7306]

If that had blown up, an entire colonel would be able to fit up the armorer's ass after that

[@clintonlayne9253]

When did the Corps start Dropping Marines or Recruits from the range ?

[@danielczech30]

@@clintonlayne9253 Safety violator.

[@rockhopper01]

@@clintonlayne9253 indeed. I myself had a safety violation and automatically failed a rifle qual in the early 90’s. I still had to stay and finish the qualification. I had to do it again the following week, where you then get Marksman no matter how well you did (I think I shot a 218, which was good enough for Sharpshooter). I guess they could drop you on the spot if you do something truly egregious, like actually shoot somebody. But that’d be weird too… “Hey, can I have that guy’s BCG?”

[@tcdnuss68]

@@clintonlayne9253 I was a PMI in the Marine Corps, Primary Marksmanship Instructor. You can be dropped from the range for safety, emergency or failure to qualify. Marines vs Recruits...separate animals, recruits are not Marines...

[@joshuabruce9920]

I'm only like 2.5 years into being a gun enthusiasts so I don't really have an opinion yet I'm still forming one. I learn something new almost everyday, I really do love KZbin as a resource for learning

[@GunWillTravel]

This is exactly why Mil Spec matters! Drop in a new BCG, and it just runs. I've never had a headspace issue, actually. But tuning the weight of the BCG and buffer with the spring and gas system definitely can affect operation.

[@marcusg137]

Mil Spec is honestly a joke.

[@P07H34D]

@@marcusg137 What is really a joke is when you buy a gun and it can't even run cheap ammo

[@crunch9876]

@@P07H34D very true

[@user-oy9zy4ds9m]

With a full auto lower i go through so many bolts and uppers so it turns into a frankenstein build really quick. Tolerance stacking certainly matters, Ive had a few bolts that would not work in certain chambers but theyd work fine in others and vice versa, all different brands.

[@caseyschryber1255]

Who asked. Pathetic flex

[@user-oy9zy4ds9m]

@@caseyschryber1255 who asked for your pathetic insult 🤣

[@theshapeexists]

​@@caseyschryber1255 this is a comment section on BCG's, so people are going to comment on it from personal experience.

[@arapahoetactical7749]

I'm a retired USAF weapons instructor and part of our job was to inspect and maintain the small arms in the inventory. We were using the old original M-16's, most of which were Viet Nam era up to '95 when we finally switched over to the A2 models. I don't ever recall seeing one go down for head space issues though we inspected annually with the gauges. The biggest issues were in barrel erosion. When we had one fail that test, we usually just turned the whole gun in to be replaced. The gauges we used on the M-16 were the No-Go Headspace, the Barrel Erosion for both chromed and black bores and the Firing Pin Protrusion gauge.

[@hairydogstail]

I have seen many short chambered barrels and why it is imperitive to use a go gauge..What size go gauge did you use in the Air Force? Colt TDP has a requirement for minimum head space..

[@chad9166]

We need a set of mugs with Steve and Caleb's likenesses on them

[@drengillespie]

With the handle being his ears.

[@carlk1183]

Yeah, great idea! Steve drinks out of a mug with Caleb's likeness and vise versa. Epic.

[@patrickdaly5068]

Awesome! I’d buy a set just because it would be funny, but also to support them for all the great info.

[@davidforce5617]

I was an armorer MOS 2111 for 10 years in the Marines and I have literally inspected thousands of M16 rifles including a 3 year tour at MCRD PISC and the amount of rifles that failed headspace could be counted on one hand with fingers left over. I dont remember replacing any BCGs but we did replace plenty of the gas carrier keys.

[@hairydogstail]

In the civilian world, short chambers are not uncommon.That is why a go gauge is required..

[@shirothehero0609]

Would be interesting to see how the M27 ends up comparing in terms of failure mode and mean time between failures compared to your previous exp.

[@syntaxerrorsix3137]

I'd wager the average builder doesn't ever check head space either. I don't, although I've had Faxon match a new BCG and barrel for me. But that's it.

[@hairydogstail]

@@syntaxerrorsix3137 The average builder??The 2 gunsmiths in this video said you don't need a go gauge when I have seen many more short chambered AR rifles in my life time ( I'm 62 years old) compared to over sized chambers..The AR world is a maze of confusion, contradictions and bad advice.......

[@syntaxerrorsix3137]

@@hairydogstail I suppose you could do a poll on any of the big gun forums if you doubt that. It's just been my experience.

[@2amichaelj]

Just so people are aware, yes, charging the handle and dry firing does break in the bcg to the barrel. You don't necessarily have to live fire the weapon in order to break in that particular bcg to that particular barrel.

[@jonathansmith7306]

How? The pressure of the bolt lugs on the extension lugs would be negligible when dry firing

[@TerminalM193]

@@jonathansmith7306 I think he means a brand new bcg. I can see dry fire and racking the bolt a few dozen times possibly removing any microscopic imperfections from factory. I personally don't do that BUT whenever I have a brand new bcg I lube the star chamber and the bolt lugs really well and then break it in with about 100 rounds before cleaning and then lubing properly.

[@2amichaelj]

@@jonathansmith7306 the bolt locks every time you charge the bolt. Every time it locks the lugs. The pressure unlocks the bolt, which is the same thing you're doing when you charge the handle. It's probably not putting as much wear as live fire but it's still breaking that particular bolt onto the chamber.

[@d30gaijin]

Far more important would be a video on mixing & matching AR308/AR10 bolt carrier groups, to include your own BRN10.

[@CrashRacknShoot]

Ar10s are a completely different animal. It isn't just an "opened up ar15", there are different patterns that companies use, and one must be aware of them before building one. Most nowadays use DPMS spec, but there's always companies out there that go Armalite or elsewhere.

[@shawnm4503]

I know they probably have to say to check your headspace for liability reasons, but I’ve never done it. I’ll probably buy some gauges just because I enjoy doing stuff like that. I’m up to 9 different AR’s now DI, short and long stroke piston, and just about all of them came with a bcg and I’ve purchased aftermarket Lmt, JP and Bcm bolts. Switched them all up, never a issue.. but again it probably is better to be safe than sorry and it doesn’t hurt to check, a guy with much more firearm knowledge than me said the AR platform is the rarest or one of the rarest platforms to have headspace issues..

[@garydowd7313]

I can say from experience back at Ft Benning that bcg’s get mixed up in boot camp like you wouldn’t believe. Somehow we’re still here.

[@Rcasca1]

Hey guy's, I learned something here today. Thank You. I was under the impression that a new AR-15 build did not need to be head spaced. Thank you for the honest information.

[@Quality_Guru]

Here is a video worth watching after this myth buster - "Brownells Tech Tip: AR-15 Headspace". Thanks for the intel.

[@SavageTactical]

It’s definitely prudent to check the headspace on used ARs and when you swap out barrels/bolts. I have seen barrels that would not pass a go gauge and have had one where the receiver extension not aligned properly.

[@cheatingdeathcustoms2244]

Always good to check. It doesn't take a lot of time and it can save you a lot of headaches. Great video.

[@OmegaBahn]

I love the interaction! Headspace gaging is so useful even if you think you're rifle you won't change astronomically between uses.

[@twssr1955]

Another informative video. Headspace is very important. Thanks for the information and recommendations.

[@disturbedmaynard3873]

If I were changing out a crucial part like the BCG, I would be checking it before heading to the range. I have always assumed you could change these out without issue, but as I get older and work with this stuff more, and with the large number of companies making parts, I would be checking it out now.

[@hairydogstail]

Short chambers are quite common compared to over sized chambers. It doesn't hurt to have the chamber checked with a function gauge or at least a throat gauge..Proper 3 bores, gas key I.D. and carrier lengths are also important..

[@BillSmith-pp9sc]

I build my AR's. Every BCG and barrel are head spaced with go - no go gauges during the build. As a rule of thumb the BCG stays with the gun it was built with, but I will swap for testing when there are issues, and I do a head space check before firing. Because I have a few AR's, my round count is very low on all of them. Thanks for this episode. Now I know I am not doing anything wrong.

[@kenneththiessen1674]

I really appreciate your discussions on these gun smithing topics. Thank you for all the good info.

[@robinj.9329]

You should always check head space. It is the one critical factor necessary for a "Safe to shoot" rifle.

[@dickjohnson7845]

I have heard several people, including two gun smiths that headspacing an AR is a complete waste of time and having headspace issues with an AR is extremely rare.

[@stickfighter1038]

Got a set of gauges for this exact reason. When I am experimenting with a new upper, I will exchange one BCG for another but after that I will treat the bolt and barrel as a set so they wear together.

[@johnmaresca69]

These 2 guys crack me up. I remember in basic my drills always saying don't lose your firing pin cause you can just use another one from another rifle. And something to the effect with the 3 metal gas seals maybe they were called. How the slits shouldn't match up cause gas will leak out. Wow 2005 was a long time ago and my memory is shot but it went something like that lol

[@evanderboynton3057]

Firing pin totally different from headspace

[@rbm6184]

@@evanderboynton3057 Exactly. Changing parts on a bolt is not the bolt itself.

[@flyoverkid55]

I own an Armalite AR 15 A2. Bought it in 2002. Shortly thereafter I learned about other makers and bought a bcg from Bravo Co. Rifle had about 200 rounds on it. Made the exchange and everything went just fine. It's still my primary, I'm keeping the round count low on this rifle and train with another " homemade " I picked up from a friend that was dissatisfied with it.

[@BigHarryBalzac]

When I was in the army I replaced barrels and bolts all the time and never checked the headspace. As long as the brand new parts were made to spec, everything should be okay. Technically speaking, I was supposed to test fire each M18 the minimum number of rounds the manual said to, but I didn't have access to ammo or a place to fire weapons. I gave the rifles back to the unit armorers, they issued them to their assigned operators, and THEY test fired them, whether they knew it or not, the next time they were on the rifle range. There's no way I would have put a used bolt in any of those rifles, even if we were out of stock. I would have told the guys to come back when we get more, ordered them, and technical supply would notify them, and me, when the parts came in. What you should do, or can get away with, is different with new barrels and bolts compared to with old ones. I wouldn't hesitate to swap bolt carrier groups between my ARs if I had any reason to, because I know nothing is worn enough for any combination to cause excessive headspace.

[@alancranford3398]

I retired from the military ten years ago and I'm just repeating what I learned as an experienced unit-level armorer: 1--don't mix up bolt carrier groups 2--armorers will MAKE SURE that all weapons are sent for annual checks and services Much of that can be institutional habits. The M60, M240 and M249 all fire from the open bolt position. The M2/HB fires from a closed bolt position. Now out of service, the M1917 and M1919 series machine guns fired from a closed bolt. Cook-offs were common with the closed bolt guns and a worn M60 sear could cause runaway gun--the measures to counter cook-offs and runaway guns were still standard machine gun range safety procedures when I retired. The "don't mix up bolt carrier groups" may be obsolete dogma. The M16 family has been in military service for almost six decades and dogma changes slowly, but does change--so perhaps the "don't mix up bolt carrier groups" is no longer a problem. Swapping parts proved to be an issue with the Reising M50 caliber .45 submachine gun of World War Two and led to pulling them from Marine Corps front line service (along with other issues) but the Reising was perfectly serviceable in the Zone of the Interior and when used by law enforcement agencies.

[@chrisb9478]

Yep, as long as you check headspace with gauges.

[@everettyost8639]

Colt factory bcg worked perfectly with your SRN 180 300 Blackout upper. Built a lower for the 300 and bought a BRN bcg for it. Worked perfectly.

[@armedfarm3429]

I've got & have run 4 - 5.56 uppers. I have 1 lower, with a bolt carrier. They all run perfect, my measured brass is within spec by a good amount, my newest has a fuzz hair less head space than the others. It is an amazing weapon system. I have SS bull, an H-Bar 20", a 18" mid-length, & a 16 " carbine. I always flippin around upper parts. Crazy

[@Tinman3187]

3:24 In my short military experience, the barrel and bolt group wared at a similar pace but the extractor gives out first. I had to have multiple extractors but only burned through one barrel and one bcg and they just replaced the whole upper since it was essentially toast. If you can afford to shoot the tens of thousands of rounds needed to wreck a quality upper you can afford a set of armorers guages to guard against bcg/lug failers. Armorers tools are easy to use if you read the instructions.

[@A8vscRrabbit]

Love these early morning videos.

[@michaelpeterson1169]

I have an old AR from the early 80's, that has easily over 10,000 rounds through it and, I have swapped the bolt carrier but, not the bolt. I've even had to change the lower parts because I was getting double fires. I also have another BCG that I swap between a 5.56 upper and a 300 BO upper without issue. Both have low round counts so, I don't worry too much about it.

[@bradleymorgan8223]

There's a spec for a reason. Any manufacturer who doesn't meet the spec is not worth using in the fist place, matched or not.

[@joshuathomas8529]

Ok so here's my simple question I bought a brand new upper from one maker and paired it with a brand-new bolt carrier from a different manufacture without using any gages gun runs fine, should I be worried?

[@CalebSavant]

The majority of the time you'll be fine, but there is a chance you won't be, which is why I can only always recommend checking the headspace.

[@joshuathomas8529]

@@CalebSavant so then the rule of thumb would be buy your upper with the bolt carrier to be on the safe side?

[@rbm6184]

@@joshuathomas8529 Yes. Complete uppers with BCGs are factory inspected for headspace to match.

[@Zestypanda]

Love the educational, entertaining videos you make. Also like that you do make videos on our questions.

[@patdennis3751]

Of course you can AS LONG as your bolt and barrel extension are within spec. Only way to be sure is a go and no go guage

[@LKaramazov]

Crazy, I’m a newbie and don’t know the first thing about headspace, and I’m in the market for spare BCGs,like this very second. I thought they were all interchangeable. A little knowledge is a dangerous thing I guess. Classic firearms just sent me an email and I was thinking about buying a .308 bcg for my PSA. So it SHOULD work, but I’ve got to use some kind of gauge. I thought they were all interchangeable. That’s why when I see these brown Ella vids, I immediately click!

[@nickstarks22]

The Ar-10 platform isn't part of a TDP (technical data package) or mil-spec like the m4 or ar15 is. There are at least 4 different ar308/ar10 patterns. The DPMS GEN 2 is the most common these days. Some parts are interchangeable, though many are not.

[@BLUELEADER78]

With the AR15 platform they all should be in spec per the given blueprint because it was adopted by the military. The ar10 or the .308 AR, whatever you want to call it, was not adopted by the military so there isn't really an agreed upon blueprint for the platform. From my understanding palmetto state has done a decent job of creating a rather "universal" ar10 platform. Some are rather parts specific. Then there's magazines. Anyhow, the point is always be safe. With a regular ar15 the parts are much more interchangeable, typically lol, than the ar10 platform. Don't be afraid to ask questions. If someone gives you hard time just move on. I'm not an expert but I won't be a jerk to someone new to shooting or any questions especially if it's safety related. Happy shooting, I hope everything works out for you and I apologize if this was too long and not in any way helpful.

[@evanderboynton3057]

It needs to be head-spaced. It should be ok but if not it could damage the rifle or you

[@fredbecker607]

To really be sure, you need go and no go gages. In reality, the modern machining tolerances are much better than they used to. That is how they get away with swapping bolts. The carrier itself should not make any difference at all.

[@DinoNucci]

You're fine. Just stay clear of chinesium.

[@murphymmc]

I've mixed a couple of BCG's , no issues, everything had very low round count, I also had a set of go/no go gauges which were utilized. Some manufacturers of gauges have their no go-gauge set at where others have their field gauge set. It might pay to check but either one will help avoid an issue.

[@falconcowboy9995]

I was mixing and matching a cheap bolt carrier group from a 300 blackout and a 556 It sheared the lugs off the bolt I bought and rebuilt a new bolt........no problem

[@russelraven7004]

I like Steve's attitude today.

[@TacticalKeene]

I have a JP Enhanced Bolt with an Adams Arms Low Mass bolt carrier for piston. Works pretty good. About 3k rounds into it now. 😊

[@nanomachines2985]

My AR build has an Aero Precision upper, PSA lower, coda evolution hand guard and muzzle break, 2A gas block, Sharp's Rifle Company BCG, a Wolfpack armory barrel, galaxy tactical furniture for the lower and buffer tube, and MFT stock. I call it my Frankenstein gun and it'll smack a target inside a quarter at distance

[@waltersobchak2973]

I bought a Ballistic Advantage 6mm ARC barrel, was quite surprised to find it failed headspace check with two different BCG's. It doesn't happen often, but reinforces why it's always important to check. (BA replaced the barrel under warranty with one that did pass a go/no-go test with the same BCG's.)

[@dtomamerican3471]

Please do video on how to head space with AR...maybe how to take out ejector and extractor on bolt to perform task. Thanks. Good vid.

[@STEVEARABIA1]

It would be interesting to see these measurements done. I’d like to know more about what’s going on.

[@erics1723]

Check out the SOTAR channel here on KZbin. School of the American Rifle. Several videos on gaging out the AR15 platform.

[@shirothehero0609]

Also check out Battlefield Las Vegas. They keep COPIOUS amounts of records, measurements and lifespans of bolts, carriers and barrels, etc., from different manufacturers and MTBF numbers. They can basically predict where, when and how a part will malfunction or fail from said manufacturer. Really fascinating stuff if you're into how things bed in together and eventual failure modes between platforms.

[@miniaturefarmer464]

I have Forster go/no-go/field gauges and check every time I swap bolts on guns to be safe.

[@barryfairwood2174]

Fort Jackson S.C. 1970, 1971 when we cleaned weapons many parts were mixed up. Nobody worried about that. The only concern was the serial number of the M-16a1 matched your weapons card in the rifle rack. Back at my Guard company in 1971 we were issued new Colt M-16a1. The geniuses at Camp Hartell engraved the bolt carrier with the lower receiver number. This was not any help. After the first summer camp there was a group cleaning, all the bolts and upper receivers were mixed up. After yearly qualification firing, not one blew up. 30 years later talking to a machinest who had a contract with Colt, making tooling for gauging, I learned something the, tolerances were really tight. Normally I would not mix bolts and upper receivers, but would check the head space if I had any doubts.

[@DonnaSeward-m7l]

I bought both the brownells GO and NO-GO gauges 10 yrs ago when i built my very first AR. Mainly because i was new to building, and i was a bit nervous about my rifle exploding in my face 😂

[@Gshockchica]

What are your thoughts on mixing bolts and bolt carriers? I.e. phosphate bolt in a Nickel Boron bolt carrier or phosphate bolt in a DLC bolt carrier?

[@adventurfly879]

I built mine on a wilson combat upper and lower and have run 3 different bcgs. Works just fine. Im using a bcm bcg right now

[@danefoss9679]

Show us how to use the Guage to measure our own headspace on an ar-15. Thanks, keep em coming!

[@guysracingsims2508]

I just learned that I need to learn more about AR platform

[@shirothehero0609]

I'll give you one more - LWRCi and Sig 516 gas piston BCGs. Interestingly enough, they use the exact same measurements for piston rod extension and bolt strike face dimensions. The ONLY difference is Sig uses an AR semi type bolt and LWRCi uses an M16 FA type. Both "separately" patented and ended up with the same bolt strike face locations. Conspiracy? Probably not. But fun fact for the day since piston systems are all almost completely unique. So if you're in a pinch, you can get one of either.

[@hairydogstail]

Well you are getting better but you do need a go gauge as I have seen many more short chambers compared to too long chambers. Short chambers will increase pressure, blow primers, degrade reliability and effect accuracy. In 5.56 marked barrels, be sure to use the correct TDP go gauge of 1.4646 and not the commercial 223 1.4636 go gauge..

[@masafarmi7709]

I have used for many years mismatch BCGs, bolts and barrels together. Never had an issue with headspacing. I have always used common manufacturers like Bushmaster, Daniel Defense, Colt etc. hey are all same sizes. Sometimes I forgot which BCG belongs to which gun.

[@invertedpolarity6890]

Vast majority of the time, the gun will be fine, will run fine, and won’t be unsafe. In a handful of cases, the gun won’t be reliable. 1 in a billion, the gun could be unsafe to fire.

[@DinoNucci]

No.

[@operator8014]

What are you suggesting will be unsafe? If it's able to fire without being locked, then it's not a part-matching issue, it's a broken component issue. What else are you saying is at risk here?

[@Kimaracustoms]

I wouldn’t say 1 in a billion. I have a few companies in mind that have consistently none concentric bolt faces that do not headspace in my nice rifles or personally build rifles built around higher end components

[@sandervanduren2779]

@@operator8014 your headspace may be out of whack if you mix bolts between rifles. If you have excessive headspace over time, the extra bolt thrust could lead to more stress on your bolt lugs which could shear off bolt lugs which could in turn lead to a very bad time for you and your rifle

[@genelyda1102]

Maybe that is why they are mil spec just like the Colt .45 in world war 2

[@shawngrays9087]

Educational, What about a video a LR-308 BCG, was curious if there is a variation between a semi auto and full auto lr-308 BCG

[@chipsterb4946]

You need to check headspace with both a GO gauge and a NO GO gauge. Too much headspace wears out your brass fast. Too little might get exciting and not in a good way. I’m glad you guys brought this up. Having ordered the parts for a second upper, it sounds like having a bolt dedicated to each barrel would be prudent. Not absolutely necessary, but I hadn’t thought about the bolt lugs and the barrel extension wearing together. One other point is that you 2 appear to be talking about AR-15s chambered in 223 Remington/5.56 NATO. There are clear military specs for every part, every dimension, every material in that rifle. 308 ARs are a whole different world. I bought a bolt and barrel from the same VERY reputable manufacturer and still had to send them back to get the chamber reamed out 1,000th + so the bolt would close on a GO gauge. (They fixed the problem quickly and all I paid for was shipping.) I think you should assume that a bolt for any AR other than an AR-15 is *not* swappable until proven otherwise with headspace gauges.

[@thomashanke6750]

Had similar issue on 308 build. Purchased barrel and bcg from same reputable company. Asked them to head space check before shipping. Was “assured” the products they sell are all “in spec”. Took a few months to get all the components together. Assembled it, went to fire it and had cycling issues and hold open issues. Had adjustable gas block, full gas and still same issues. Checked the spent brass(new factory ammo, brand name) the face was gouged and small brass shavings on the bolt face. Bought head space gauges. Sure enough it would not close on a “go” gauge! Sent it all back for them to “investigate” it. They replaced the bolt. Pissed because I even requested a head space check and was blown off. Was 2 months before I got the rifle back together. Barrel and bcg came from a company that’s owned by the company that made the upper and lower I used. Figured that would help with compatibility issues. IMO the companies are pushing out products too fast and not having the QC from before.

[@chipsterb4946]

@@thomashanke6750 I must say that Fulton Armory couldn’t have been more helpful and turned the barrel reaming around really fast.

[@hansoak3664]

This was pretty much my opinion as well prior to watching this video. I was always a bit more cautious about round count but I have nowhere near the technical knowledge that these gentlemen have so I am relieved that I was perhaps being a bit too conservative regarding round count.

[@johnmorganjr769]

😂 "Take a sip, Ill do the lifting" 😆. (Thank y'all for moving a county over ! Davie Co., N.C.!)

[@charlesdavis3923]

I had been told bolt carriers were all about the same so when I bought a couple of ar's I switched bolt carriers out and mix matched bolts in guns I built before I heard anything about head space. Luckily I never had any trouble

[@Meat_Demon]

I built a BCG from components from a myriad of manufacturers. Sharps, Pof, V seven, JP enterprises. Its a sweet bcg.

[@christopherspindler6328]

For the uninitiated, could you do a video on how to check and adjust headspace?

[@khann844]

I don't know why they didn't include that.

[@cutwormsmith]

I don't think u tube will let them.

[@Watchdog_McCoy_5.7x28]

The only practical way to "adjust headspace" on an AR is to buy a new bolt or barrel, and check it again and hope it's right. There's no "adjustment" as the locking lugs and barrel extension "are what they are". You can technically machine the bolt or barrel extension to proper dimensions, but that's above what most people are willing or even capable of doing. I've never seen or heard anyone have any issues with headspace on any AR from a reputable manufacturer, and I've been shooting ARs for 35 years. I've swapped barrels and bolts around between guns all my life (Im speaking of ARs only. Most all other guns definitely need headspace to be checked), and never checked headspace, and never had or heard of any issues. It doesn't hurt to check it, but the manufacturing processes and the nature of the way an AR bolt and the barrel extension mate together, it makes it so this is virtually a non existent issue. Roller delayed and roller locked firearms are more prone to have headspace issues, due to the design, as well as other types of of blowback, lever delayed actions, etc. Do some research though, and don't take my word as gospel.

[@richardackerman838]

I've been wondering about this topic. A friend asked me if he needed a spare BCG. I told him, if I had an AR, I would want a spare. I had heard that bolt lugs break off, or firing pins wear or break. I'll relay the message next time I see him.

[@rj8288]

I had a supply sgt who did not number the bolt to the receiver. Within two trips to the rifle range we had 50% of the bolts had cracked lugs. It is not head space, it is the individual form fitting of the lugs to the receiver barrel extension. After a number of rounds fired, each bolt is perfectly matched to the barrel extension. Switching bolts to a different gun re sets the bolt lugs and cracks start forming. By the way, I have been shooting an M-16 since 1968. I think that I know what I am talking about.

[@hairydogstail]

The support I.D. bore in the carrier and the O.D. of the bolt support shoulder determines how square the bolt sits in the barrel extension..Each carrier can be different putting strain on different lugs when switching bolts..

[@gnusasg]

Getting even a no-go gage is cheap insurance IMO. After all the parts I've switched around over the years, I've only had one bolt that closed on a no-go but you can bet your ass I'm happy that I caught it.

[@ethan5.56]

I purchased a bunch of parts for a new AR pistol project but my new bolts gas key wasn’t compatible with my new gas tube so I swapped to another bolt from another AR and the headspace checked out with both bolts. Haven’t had any issues with either gun since the BCG swap. Great video as always

[@hairydogstail]

Your gas key could have been bent or the bolt carrier was not milled square for the gas key.. The bolt has nothing to do with the gas tube..

[@ethan5.56]

@@hairydogstail works fine with the other rifle. Both bcgs index with the other gas tube just fine without any resistance. One just wouldn't work with the overall diameter of the gas tube

[@ethan5.56]

And by bolt I mean bolt carrier in general I know the bolt head doesn't have the gas key on it

[@hairydogstail]

@@ethan5.56 So you are saying the gas tube was too big, or too small to fit into the one carrier's gas key?? You did say bolt's gas key, not carrier's key, but I now understand what you meant..

[@ethan5.56]

@@hairydogstail yes either the carrier key was undersized or the gas tube was too large for the Faxon BCG. Pulled out one of my young manufacturing BCGs before installing the gas system to check compatibility and they mated together beautifully. It wouldn’t even start to go in the faxon carrier key but the faxon carrier key works fine with the gas tube in the other rifle

[@lookingattheman]

Thank you guys for making these great videos!

[@Googleaccountt]

You absolutely should check headspace on a new build. 90% of the time, the headspace will be perfectly fine between the barrel and bolt. Where it gets dangerous is after a few thousand rounds, when the bolt and barrel extension have worn down material, and your headspace is excessive enough to cause the brass to expand to the oversized area and it blows up in your face. My personal preference is to check any new rifle with a 5.56 go, a .223 no go, and a 5.56 no go. I swap bolts until I find one that lands in between the 5.56 go and .223 no go..That yields longevity in terms of the headspace after a couple thousand rounds. Gauges aren’t particularly expensive, and there’s no point in blowing up your gun that spent good money on. For anyone saying they swap bolts or “go off of feel”, you’ve just been lucky so far, and the difference is in the ten-thousands of an inch, so I’m highly doubting your spidery senses can tingle that one.

[@josephraymer783]

Great information guys. I’ve been shooting lever guns for years and built my first AR this year. I have less than a 1000 through it and was was wanting to upgrade the BCG from a black palmetto to a chrome Aero precision and was wondering how it would affect performance.

[@Skinski7]

Just easier to clean I would think.

[@lynnhunley7597]

No willy nilly bolt changing without a check, got it. Thanks!

[@operationalaf3414]

I always headspace my AR15 barrels. Never had a bolt not headspace though. I don't mix and match my BCGs just because I don't feel like swapping stuff when I grab a rifle. I would trust 5.56 over an AR10 though because specs are all over the place compared to 5.56 which has been standardized.

[@albertptran]

Good topic, i was thinking of running the same bcg in two uppers

[@RobinP556]

The number of rounds that affect headspace…42, the answer to life, the universe, everything. 😁

[@georgesakellaropoulos8162]

So long, and thanks for all the fish.

[@cliffkirby8570]

Good information to have because I've been looking for a bolt and a extra set of gas rings for a Daniel defense M4A1 with very little luck, I really don't want to mix and match some aftermarket part for that gun but looks like I may have to, no service companies seem to have phone numbers anymore just email addresses

[@realisrealite5554]

Just buy a DD bcg

[@frickenbored]

I bought a go/no go gauge set and check headspace everytime i change a bcg...its just peace of mind.

[@jcows12]

I have several and have swapped bcg without any issues however I use them for hunting and occasional plinking not heavy use of rapid fire so I can see where shooting 1000s of rounds could cause wear making swapping problems arise.

[@marzcapone9939]

I've got my LMT MRP and MWS barrels mated up with their own bolts. When I bought an extra barrel, I got a new bolt to pair up with that barrel. I've never checked head space, probably should.

[@iradale4855]

Every time I see these videos and see that AT-4 it brings a smile to my face lol

[@350volvo]

I think as long as you check head space you should be totally ok. The one issue you could run into is the tolerances of the bolt to the BCG ,either giving you a more or less effective gas system.

[@Vuntermonkey]

I've assembled 2 ARs and didn't check headspace on either. I honestly didn't even think about it since I trusted the manufacturers. I guess that was an acceptable risk to me, but I understand why you should probably check.

[@tjbray72]

Thank's ...Enjoy watching

[@hondasaurusrex6998]

People at Brownell's should make and sell a coffee mug with Steve and Caleb holding their coffee mugs.... just a thought. And as always a great video.

[@welderdude1]

I have swapped BCGs between my collection of AR15s to verify head-space. All of these have been done with low round counts though. For my battle builds I only swap the bolts if and when I have an extractor failure and don't have a rebuild kit on hand.

[@2afreedom1776]

Caleb, you should post a detailed video how to head space- step by step!

[@CalebSavant]

We have it as part of our build series.

[@2afreedom1776]

@@CalebSavant link please

[@realisrealite5554]

When I build a rifle I never use the same mfg for the barrel and bcg.I always use a premium bcg DD,Lmt,Colt, ect.Ive never had a problem with any build.Some times I mix and match them on the builds with no problems.They run like my Colts,Urgi,and Fn factory rifles.

[@solomonsgtjustinl9724]

My opinion is I ain’t got no opinion, and I own three ARs. But, thanks for the learning, boys. Now I’m off to find me a go/no-go gauge.

[@PunkN_JTM]

Saw a redit pop up , Asking , when should someone refill their gas piston... I couldn't help but lol... Talk about a walk of shame going to the range with yer buddies and forgetting to fill up with piston gas .🤣🤣🤣🤣

[@fredbecker607]

The military used to be very serious about not swapping m16 bolts around. Meanwhile the m60's swapped barrels regularly. Reality was the bolts got swapped and we didn't have any gages at the unit armorer level.

[@Valorius]

I've been mixing bolt carrier groups from various manufacturers for, i dunno, 20 years.

[@russhayes4882]

Love your videos great stuff as always

[@TerminalM193]

I mix and match bcg all the time. I noticed IMMEDIATE improvement in my Ruger ar556 after swapping the bcg to a full auto sons of Liberty Gun Works phosphate bcg

[@Vuntermonkey]

Interesting. What improved, specifically?

[@TerminalM193]

@@Vuntermonkey brass ejection was much more prominent and went from 2 o'clock ejection to 3:30 ejection pattern, perceived recoil felt better and less malfunctions, "so far". There's probably 4k rounds on the rifle, 1k of it being with the newer bcg. I've been thinking of playing around with the buffer just for the hell of it since it's primarily a range gun. My 12" BCM hasn't been modified at all other than attachments.

[@blackhawk7r221]

The bolts and BCGs as a bulk whole are manufactured to certain dimensions, not hand fitted. They are interchangeable with any barrel extension unless you have a custom match set like a headspaced Wilson. When Bush came out to visit us for Desert Storm, the entire Battalion had to give up our BCG. Should have seen the boxes of them. Of course, no problems when reissued.

[@trevorferguson8271]

5:26 Can you do a video on how much clearance is to much for the bolt carrier group contact points inside the upper. If that makes sense. All my ARs the bolts have a good bit of wobble when in battery, and this is when I separate the upper from the lower.