Thoughts on Accurizing AR?

[Clint]

Sure. You take a bunch of bolts. Remove the ejector from them. Put the one of the gauges (for that barrel length) into the barrel. See if the bolt will lock. Repeat till you find one that does.


C4

How does barrel length change the desired head space?

[TacticalFun]

Im not sure about the rest of it but we have been pressing hanson premium 18" barrels into bcm uppers and head spacing the bolt on our newer competition rifles. Paired with ssa-e and the new ssp triggers our shooters are shooting consistent 1/2 moa.

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[EzGoingKev]

Joe Carlos, a gunsmith who specializes in building match grade ARs for Service Rifle competitions talks about barrel to receiver fit, including a couple of ways to improve it. He mentions that he has seen group size improve by as much as 30% when a loose barrel to upper fit is corrected.

He talks about swapping the barrel extension out for an oversized one to tighten up the fit. It kind of comes across as spin the extension off and just spin the oversized one on. I would think that it is more involved then that as the barrel extension's pin needs to be in phase with the gas port.

I used to lap the receiver face, etc. Then, a well distinguished high power shooter said that either the USMC or AMU stopped the practice as they saw no real benefit to the practice.

I do not think lapping the receiver base increases accuracy. I do think it squares the barrel extension to the bolt face so the lugs are all loaded evenly instead of being biased to one side.

Use a hair drier or a heat gun on those tight uppers to get the barrel in.

A cup warmer works good for stuff like that too. Place the receiver face down on the cup warm and let it sit a while.

[26 Inf]

I've used BCM blem/demo stripped uppers for north of a dozen builds, using barrels from various sources - green mountain and ballistic advantage mainly.

The extensions fit snug in the receivers, but I've never had to freeze the barrel or heat the receiver.

Do you think it is because the receivers have been previously used on demo rifles?

[TacticalFun]

I've used BCM blem/demo stripped uppers for north of a dozen builds, using barrels from various sources - green mountain and ballistic advantage mainly.

The extensions fit snug in the receivers, but I've never had to freeze the barrel or heat the receiver.

Do you think it is because the receivers have been previously used on demo rifles?

Yes. Usually you either need to sand the inside of the bcm or heat it. I actually made up a jig to press the barrels in.

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[HelloLarry]

From what I understand, one of the nice features of the Joe Carlos/Shilen barrel extensions is that they are cut with a thread that begins at the same spot on all of them so they are truly interchangeable.

[EzGoingKev]

From what I understand, one of the nice features of the Joe Carlos/Shilen barrel extensions is that they are cut with a thread that begins at the same spot on all of them so they are truly interchangeable.

If you are Shilen and you are making your own barrel and extensions I can see that being the case.

Maybe I am wrong about this but I do not see that happening 100% of the time when using a barrel from company A and an extension from company B.

I would love to hear from someone who has actual experience swapping these things out.

[Jsp10477]

I've used BCM blem/demo stripped uppers for north of a dozen builds, using barrels from various sources - green mountain and ballistic advantage mainly.

The extensions fit snug in the receivers, but I've never had to freeze the barrel or heat the receiver.

Do you think it is because the receivers have been previously used on demo rifles?

I’ve built several uppers using bcm receivers and had to heat every one. I’ve used Krieger Direct, a CLE Bartlein, Lothar Walther, a few ARP’s, Colt, and Ballistic Advantage barrels. A heat gun or propane torch gets it done. I haven’t used the blem uppers.

[JediGuy]

Grant's recipe for success;

*NOTE, assumptions are made that the builder will be using KNOWN, QUALITY barrels, receivers, etc.

1. Tight fit between barrel extension and receiver.
A. You can use loctite, but assume that if Green is used, you probably won't get it back apart.
B. Just use a BCM or VLTOR receiver as they specifically undersized the barrel extension hole (tight fit).

2. Check that the upper receiver M1913 rails are square and true.
A. We use a Tru-Stone from Starrett to verify.

3. Barrel nut is at or under 40lbs.
A. You can use shims if the barrel nut design doesn't allow for correct timing at that poundage.

4. FH/MB is timed (5 O'Clock position) so as not to put to much pressure on the end of the barrel (which causes "trumpeting").
A. Use shims to time.

5. Fit bolt to barrel extension. J. Noveske taught me this (along with ranges for each barrel length and gave me the gauges he had made).

6. Square and true the barrel and then re-crown (30 degree).

7. Be a good shooter! Use a good trigger! Use good ammo! Use good glass! Well, Duh! ;-)



C4

As someone who is not particularly knowledgeable but pretty good at following instructions, this summary seems like a great opportunity to build out an article or (if you’re into it) a step by step video. Not that it’s needed, but I would find it helpful to “see” these things done.

[e z money]

Reply to original post. Quality ARs and army issued M4s do their part better than the shooters do. This is true for they army, if you want to, not just hit a silouette at 300 meters, but hit it between the eyes, you need to get a sniper rifle. A quality AR is already accurate.