Barrel nut re-torque & accuracy

[Pathfinder]

Thought I'd share my experiences since apparently the 450 isn't immune to this malady. I recently switched out a 450BM barrel because of a rough chamber. I couldn't seem to dial in a load the new barrel liked. Factory ammo wasn't any better. Nothing better than 3 moa was a disappointment compared to the 1 moa my "bad" barrel had delivered. Checked all the usual suspects with nothing standing out.

I recalled a 6.5 Grendel build that I had to torque the barrel tighter than I'd liked to index the gas tube. It wouldn't group either. A friend with much more experience than I suggested re-torquing the barrel. I ditched the conventional barrel nut and used a clamp on handguard so I could use whatever torque I wanted, (I normally use 55 lbs) and suddenly it shot great, and still does !

I thought I had torqued the new Bushmaster barrel to 55 lbs, but I tore it down and re-torqued the barrel anyway. Magic ! Back to one ragged hole today. My friend told me he's done that with several rifles that started to lose consistency over time as well.
Anyway, it's a simple thing to try if a new build isn't up to snuff, or if a usually accurate rifle loses it's edge. I didn't touch the gas system or break the barrel loose from the receiver. Just loosened the nut & re-torqued it. Maybe it's the change in torque, or maybe it's just re-seating itself, I don't know. I just know it's made me much happier twice now !

[Buckeye45]

Very good point. I too have had this happen. Both with 450 and 556. I try to tell my friends to avoid the cheap Chinese rails with the aluminum barrel nuts as this seems to happen a lot.

[Pathfinder]

Very good point. I too have had this happen. Both with 450 and 556. I try to tell my friends to avoid the cheap Chinese rails with the aluminum barrel nuts as this seems to happen a lot.

I've heard of aluminum barrel nuts, but have never seen one.
All my cheap rails came with steel barrel nuts.

[Hoot]

If I cant get the gas tube to index close to torque spec without going over, I add the necessary Barrel Nut Shim(s) to get it there. Never had to re-torque a barrel. I do however tighten, loosen and re-tighten a few passes to work the anti-seize into the threads, both coming and going. Just best engineering practice. The Barrel Nut Shim Kit isn't expensive but a galled, cracked, warped or otherwise ruined receiver is. I have used both steel and gloss anodized aluminum barrel nuts. Taking the first hole alignment past 35ft lbs won't endanger either kind. Going past 50 would be pushing your luck with aluminum but you should never have to go that high with the shims. I have done several 24" bull barrels and due to their leverage, I have favored steel nuts, north of 40ft lbs for good measure.

Come to think of it, I did re-torque a barrel once on a 300 WSSM AR 15 after 200 rounds. Started out just on general principal but discovered that it needed it. Its recoil made my 450b feel like a 6.5 Grendel! I wound up putting a Ross brake on it and that had a much more noticeable effect than adding a Ross brake had on the 450b's I own. It sure did turn heads up and down the covered firing line when I touched it off however.

If you frequently build or service AR's, you really should have a set or two of those shims on hand and No, a carefully cut aluminum pop can won't do.

Hoot

[MiHunter]

Pathfinder,

When installing an ar barrel i usually have the receiver surfaced at the receiver to extension mating surfaces. My local shop does this for $15. Secondly i always "bed" the barrel extension into the receiver with blue loctite. The ideal fit would be a thermal fit but with all the different uppers and barrels out there its hard to find that. By doing those two steps ive personally seen better consistancy in my rifles. Heres a link to read up a bit on bedding if interested.
https://americangunsmith.info/2013/04/0 ... 15-part-2/

[Pathfinder]

Thanks for the input ! All good practices.
I do "season" the threads by tightening at just below 40 lbs several times before my final torque.
I also "bed" my barrel extensions to the receiver with blue loctite.

I started exclusively using the clamp on hand guards just to take indexing out of the process altogether.
It can also allow barrel removal or re-torquing without moving the gas block off the port.

I also usually loctite the shroud to the barrel nut before final clamping. I've not had a barrel nut move yet, but I figure that would give me immediate visual indication since the picatinny would no longer be aligned.
So far all the loctite hasn't been an issue as far as disassembly is concerned.

Are there compelling reasons for using indexing barrel nuts instead of clamp-on designs ?
I can't think of any, but I don't know what I don't know.

[MiHunter]

Like you i try to stay away from a barrel nut you gotta juggle around trying to line up the gas tube and get the right torque. I cant think of a reason either that would be beneficial using one over the other except for ease of gas tube alignment.