AR Upper/Barrel Play?

Full Clip · Oct 8, 2008

I have a carbon-fiber carbine upper that has a wee bit of play between the metal barrel/chamber and CF. If you twist the handguard/barrel, there is about 1mm of movement LtR. And it is NOT a loose handguard or sight block. Looking through the ejection port, I can see the tiny movement between the chamber and CF. Is this something that be tightened or has there been some sort of separation between the CF and the barrel that is a real problem?

havoc7usmc · Oct 8, 2008

Carbon Compression

I would stay away from CBF uppers, lowers maybe. Carbon will compress slightly in some cases and does have some issues with long term use. Remember, carbon fiber comes in various grades and the firearms industry, or the consumer is not ready or able to afford the cost for what a good carbon upper should be made of.
I will agree that carbon fiber is some damn good stuff when used in right application. Until JB weld sells carbon patch your stuck with, and soon to increase, slop between the upper and the barrel extension.
Sorry for the gloom & doom.

Full Clip · Oct 8, 2008

Appreciate the straight talk. Was suggested elsewhere that I check the barrel nut, tighten if possible (without stripping).
Actually, I've used JB to fix the rear pivot pin hole on this upper already. The fit with lower was way too loose, so I just cleaned and filled the hole with JB, filed flat when dry, and then re-drilled hole for pin. Fit is nice and tight now. Has worked for about 1K rounds.
JB is great stuff.

nicholst55 · Oct 9, 2008

I have no experience with carbon fiber uppers. That said, I was researching them on Bushmaster's website this morning. They insist that you send your CF upper to them for rebarreling, because they use a 'special wrench.'

I was considering using a CF upper for a lightweight 6.5 Grendel that I want to build, but it doesn't look too promising for that reason, among others.

Full Clip · Oct 9, 2008

We'll see. I have a wrench and action block on order.

havoc7usmc · Oct 9, 2008

Carbon Fiber

I'm not bagging on JB weld by no means, it's saved my butt a few times with some dove tails and other odds and ends. My concern, I would have to see where the wiggle is, that you may have a receiver that may not be to spec and ethier the ID of the barrel lug or the threads are short, not enough threads, in which case tightening won't help. Bushmaster shouldn't have any problems fixing it for you. Good luck and keep me posted

Full Clip · Oct 10, 2008

I've had the upper for about two years and only recently noticed the looseness, so I have some hope. I've also swapped out the handguards like half a dozen times and replaced the gas block/sight and gas tube, so perhaps that loosened up the nut just a bit.

havoc7usmc · Oct 11, 2008

Carbon Fiber

I don't know what they would recommend for torque spec's on carbon fiber. I generally set mine at 40 ft lbs. I'm still leery about the carbon fiber uppers but I would use the lower. I know the teaching M16 / M4's that we used in the class room have been taken apart and put back together hundreds of times, including taking off and reinstalling the barrels, and they have very little slop, except for the roll pins which take a beating. IMHO, I don't think the carbon fiber could hold up to that much dis assembly / reassembly.
I think the carbon fiber would be fine for civilian use and maybe varminting but I would never use it for tacticle or military use. If it was that good the military and Colt would of picked up on it years ago. Carbon fiber has it's place but I don't think it's with the uppers just yet.

AR Upper/Barrel Play?

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