MK12 MOD 1 SPR - Building The Upper

[@mike5523]

This is exactly what I need. I’m planning on building a mk12 upper to put on my Saint Victor lower. I love the AR platform

[@Mr2ndAmendment]

It looks great, I'm wondering about the barrel nut though, did you season the threads off camera? You need to tighten and loosen three times total with a torque wrench to properly season the threads of the upper. You use a torch wrench attached parallel to your armorer's wrench, you go up to 35 lbs to match up the gas tube, then loosen. Each time you do it you'll be able to go a little bit further in rotation, and you do the final tightening on the third time, not to exceed 80 lbs. Failure to do so can result in an eventual loose fit over time, since the barrel nut was not fully tightened to its fullest extent. We test for this by dripping CLP inside the upper around the seam where the barrel extension meets the upper. You then flex and apply hand force to the barrel and if you see bubbles or the oil being disturbed, you know the barrel extension has a loose fit. It generally won't be a safety issue, but it's an accuracy issue. The marksmanship unit dudes get oversize barrel extensions and press them into the uppers, but you can correct the situation by shimming and hand-fitting a barrel extension that's too small. We use anti seize compound on the threads of the upper, and when testing the gas tube alignment, we insert and reciprocate the BCG to ensure the gas key has no issues before we lock it down for good. Also for timing the muzzle device, I like to use a flat metal ruler and a straight wood stick. I place the ruler on the 1913 rail of the upper, then insert the wooden stick in the device. Looking from the muzzle end, you'll see the ruler on the upper as your true surface, and the long wooden sick inserted in the device will extend out each side, allowing you to ensure both the ruler and stick are totally parallel. Of course with crush washers you want to never have to loosen, so you get close and slowly tighten till the ruler/stick are perfect. This method allows a true timing while also removing the need to bust out any levels. Just some armorer tips, we don't work on Mk12s but some universal AR rules are worth mentioning. How does it shoot? Edit: I forgot to say that the clam shells are good, but the Geissele Reaction Rod is the best way to go to avoid flexing or destroying an upper. It's really the best thing out there that I'm aware of four this kind of business.

[@trigger357]

Thanks for this. I ha no idea i'm in the middle of my MK12 build now

[@dsfssdfs7395]

you know that whole seasoning the thread is complete horse shit and so is torquing it to a specific torque.During the time when the m16 was first being produced they didnt use torque specs that we have today, they just used a wrench to tighten it down and they didnt use grease and guess what the guns functioned perfectly fine.

[@meidamx]

Any issues with the crush washer and a suppressor?

[@opmike343]

@@dsfssdfs7395 The rifles being built today are better than the ones from 50 years ago. They are more accurate. They are more reliable. They are more durable. These are facts that are not controversial. Technology and methods march on. We advance and evolve these technologies. So simply reducing this all down to anecdote from decades ago of "they worked fine" is completely missing the point.

[@DowntownDeuce2]

@@dsfssdfs7395 Provide a single source citing Colt, ArmaLite, H&R, Hydramatic, Sullivan or Stoner for that ridiculous speculation. Oh, wait, you can't... Nobody is interested in the ramblings of a child who thinks an anagram is a witty, suitable, screen name. Stick to Palmetto State and Olympic budget builds on your polymer lower; they are commensurate with your level of expertise. The Department of Defense armorers and M16 TDP disagree with you; but what do they know?!?

[@hershel_van6546]

Great vid! Thanks for the parts sourcing info too!

[@Radvous]

Excellent build, thanks for sharing.

[@blugrassmaniac]

Awesome build! If you get the suppressor you need to take off the crush washer and time it with shims.

[@meidamx]

blugrassmaniac torque ?

[@rednecksniper4715]

@@meidamx long as it’s snug and it’s timed it should be fine long as you get at least 5 turns on the suppressor you’re fine just don’t use the crush washer use the shims that come with the brake

[@meidamx]

@@rednecksniper4715 Thanks! I actually used a one piece break/collar adapter from Otter Creek Labs. Only 400 rounds, but no shifts.

[@w.w.9047]

@@meidamx20-30 ft lbs for any and every muzzle device.

[@johng9431]

Awesome. Makes me want to build my own.

[@stevenr6539]

Awesome video. Currently building one but in 6.5 Grendel. Any issues using the crush washer with the ops break when it came to suppressor alignment? Thanks!

[@opmike343]

You should use aeroshell or something equivalent on the barrel nut. It's also a good idea to bed the barrel to the upper receiver. Something like Loctite 620. Bedding has ZERO cons when done properly and potential pros. Especially for something like a Mk12.

[@tomacton6718]

i disagree. with correct spec parts bedding is unnecessary. a coating of anti-seize on the extension and trueing the receivers face works better to enhance accuracy.

[@LRRPFco52]

​@@tomacton6718Review fleet AMU data in the re-education camp. Bedding works with many samples to prove it. In every instance where I have tested before and after, I've seen groups shrink from 1.5" or 1.7", to .6" to .7".

[@19doggydog]

What barrel did you use for this project?

[@SouthWestGunnerOfficial]

Crush washer? Not using shims?

[@sportsmanslegacy]

I know this is old but i thought the same thing. Maybe because the AEM5 and or OCM5 suppressors have the Ops Inc collar you can get away with this. The threads are on the Ops Inc brake but it buts up against the collar and that taper helps it get the proper alignment. Would love if someone else with mk12 knowledge could chime in here though… 🤔

[@SouthWestGunnerOfficial]

@@sportsmanslegacy i have a mk12 mod 1. Ocm5. I use shims. Obvious reasons lol. If a muzzle break lines up incorrectly it doesnt matter if its over the barrel or not, the suppressor will be at a degree that can cause minor to serious damage. When using a suppressor ALWAYS use shims

[@sportsmanslegacy]

@@SouthWestGunnerOfficial that’s what I’ve seen in my experience too. Just didn’t know if it was different with an over barrel suppressor as I have no experience with them lol. Thanks for the reply!

[@SouthWestGunnerOfficial]

@@sportsmanslegacy no problemo! Just want people making smart choices and not having their guns or attachments getting messed up ya know. It aint cheap and we all work very hard for this stuff. Hope everyones just safe and enjoying their time at the range 🫱🏻‍🫲🏼

[@dontask8979]

Did that roll pin for the gas tube. make it past the tube? (2:40 ish)

[@lunargentleman3750]

Dont ask ... doesn’t look like it does it

[@jmedlock95]

i didnt see you lube the barell nut threads. did you? i hope so

[@cagrangersealninja3720]

No aeroshell. Not clone correct 😉 lol

[@MushroomStampGalactica]

Uh... small world huh Mr. Rogers...

[@matts.1758]

Where the vid on the completed rifle? I'm doing a very similar build and want to see how it looks!

[@HouseHoldOil]

Coming Soon :)

[@eagle5kilo598]

Idk if this can be done on a 308 barrel and if so how long should the barrel be? 16? 18 inch? Planning on build one.

[@moistcakebytheocean3442]

Hope you know what you're getting into. If you do a clone correct PRI MK12, then you are gonna be shilling out a fare bit.

[@shizukaryujoukai2465]

My aem5 supressor collar doesn't freely slide on the barrel. Should I just heat it up?

[@HouseHoldOil]

From what I remember the barrel should be machined to fit the collar. If it is close, heat may work.

[@WildArmsResearchAndDevelopment]

Looks good, I want to do a similar build

[@HouseHoldOil]

Thanks! This was a fun build and it shoots great. I'll be posting another video at some point with it in action.

[@jacksuquett1191]

Quick question. The collar is tightened down with a set screw with the collar tapering at a angle with the barrel? isn't that collar going to walk on down if you shoot it enough without a suppressor attached? I was never really big on drilling the gas blocks and barrel and than pinning it like you see most people doing now, since the area where the gas block attaches on the barrel is actually turned "square" in relation to gas block even though the rest of rhe barrel may be tapered. All of my AR uppers now have the gas Blocks pinned to the barrel since i actually purchased a complete upper with that already done, and did find it much more secure, even though none of gas blocks have ever walked out on me. it was just one of those warm fuzzy feelings you get when atleast I feel there is one less thing I don't ever need to worry about. That collar though did leave me feeling a bit anxious.

[@HouseHoldOil]

I haven't heard of anyone having issues with the collar walking. The collar will rest against the barrel profile similar to the gas block so the set screw should hold it in place.

[@itallafuckingjoke]

@@HouseHoldOil i emailed Allen engineering about the install of the collar and they recommended one drop of blue or green loctite under the sleeve .

[@unarmedwarwolf9384]

Shame, Didn't even use any Aeroshell, torque wrench, or properly align the gas port on the barrel!

[@hgarza1136]

I was thinking the same thing. Didn't want to say anything, but it's not gonna be good if someone watches this to do theirs.

[@slack3r21]

Ok, over 2 months in and still no video on the completed rifle. How does it shoot? How is accuracy? Don't tell us, SHOW US ;)

[@redteam9881]

I built my MK 12 Mod O completed about 3 years ago ............and I started it in 2010. I used the Douglas MK 12 barrel .......the carrier full auto but I had the WMD put their good NB finish on it. My bolt is a Sharps Relible Bolt with a McFarland One Piece Gas Ring along with 5 Coil extractor spring with black insert. I put a POF Roller Cam kit on the carrier. The Firing pin is a Titamium pin which compliments the SSA-E trigger. I also install a Viltor A5 stock system with a Tubbs Flat Wire buffer spring........sure is the best AR I have ever shot after 26 years in the military sure wish I had this then. What a tack driver the MK 12. My handload of IMR 8208 of 23.8 with 77 MK.

[@Lilbaanee]

Do you need that plastic part for the knights armament rail

[@anasiangirly]

Do you true/lap the reciever

[@300balake_3]

He's blasting Taylor Swift! Lmao love the build man!

[@marcsantos5524]

What kind of armourers wrench did you use on that build! Badass build BTW!

[@yohankim8189]

where is the lower video?

[@aol328]

What barrel is that?

[@HouseHoldOil]

Douglas MK12 Barrel

[@apolloex00]

Did you only put one socket screw on the gas block?

[@HouseHoldOil]

I used both.

[@seanbrenner7813]

What knights rail is this? Been trying to look but can't find it anywhere

[@HouseHoldOil]

Check out my MK12 parts video, should help you out.

[@kalenkelly6399]

the rail is the Knights Armament RAS. you can find one on Operation parts website. be prepared for sticker shock

[@AILDdrums]

So sexy, I've got parts in the mail for this build. Still need to get the rail, arms scope rings, and a scope.

[@AILDdrums]

I'd also like to reiterate the point about the rail collar at 4:25 . I did that a little bit when torquing the barrel nut, and a put a good little mark in the collar after accidentally tightening it against the receiver. Don't be like me! Pay attention! hah.

[@tacratt6091]

When you put the gas tube through the nut,does that make the rail line up with the rail on the upper receiver, I just got a rail like this one.

[@mianelucienlara7995]

my dream rifle mk12..wish i could have one of that :(

[@dontask8979]

What's the part in front of the gas block? Anyone?

[@ellijahsmith4445]

Dont ask it’s a tapered collar that’s part of the muzzle device. The Allen engineering suppressor slides over the muzzle device/break and then the sits onto that collar in front of the gas block. It’s tapered so you get consistent suppressor alignment every time you screw it on. It also wedged the can into that piece in front of the gas block so it doesn’t walk off when shooting.

[@IDFWU650]

What grit sandpaper did you use to sand the barrel with? Thanks

[@JJ1st506th]

Are you from ohio?

[@holyass242]

What thread locker are you using?

[@darrinray550]

I hope you decide to dimple that barrel or, if you have a drill press, pin it. I pin all my gas blocks.

[@isaidme0]

darrin ray he said it already came already dimpled.