AR barrel extension to upper fit issues

[doverpack12]

I have an AR barrel that didn’t shoot well but is a relatively expensive barrel and generally considered accurate. When installing, the barrel extension got extremely tight in the upper for the last 1/4-1/8” to the point I had to put the barrel nut on and use that to seat the barrel then backed off checked and torqued.

Well after 50 plus rounds and 3 different ammo varieties it’s not shooting as well as it should, actually bad with two varieties. I changed scopes not really a change.
Lower and upper with different barrel are excellent performers.

What I’m trying to figure out is if it’s worth finding a different upper that isn’t so tight or if maybe the bolt/headspace was off or if the barrel is actually the culprit. There is one more ammo variety I could try but at this point the barrel has been pulled so I would need another upper.

 

[doverpack12]

Messed up and thought I was in the firearms forum. If a mod sees this and could move that would be appreciated

 

[flyfisher117]

Generally a tighter reciever/extension fit will lead to better accuracy. That's why guys get giddy about thermal fit uppers. Others will bed their barrels into the upper.

Personally I have seen little to no discernable difference moving a quality barrel from a sloppy Aero reciever to a thermal fit BCM reciever.

 

[Eric_F]

A tight fit has been shown to be better, if you're having issues I'd look elsewhere.

 

[Trout&Buck]

Not sure if you have already checked this but if you are using a free float handguard it wouldn't hurt to make sure that it isn't contacting any part of the barrel or gas system.

 

[RockAndSage]

the barrel extension got extremely tight in the upper for the last 1/4-1/8” to the point I had to put the barrel nut on and use that to seat the barrel then backed off checked and torqued

This concerns me, as it indicates a lack of true in the bore of the upper, with the inner diameter walls not genuinely being parallel all the way, and also likely not being uniform in how it tapers. This is not the same as an intentionally-designed thermal fit. Those have more or less properly true, parallel sidewalls.

What that can easily result in, is your barrel not fitting precisely flush against the receiver - leading to the barrel's bore being misaligned to the bolt.

That leads to bolt lugs not mating flush against the locking lugs on the inside of the barrel extension, with one side being higher or lower.

That leads to inconsistencies in how the cartridge sits in the chamber both before and during firing, and what the bullet is doing when the force of firing is first applied to it. This misalignment can cause the bullet to move forward without its axis being parallel and true to the bore axis - leading to less consistent flight.

The first thing I'd do is pull the barrel and properly lap the upper. Brownell's sells a kit for it that's around $45, IIRC, and it's fairly simple. Plenty of videos on YouTube that cover how to do it right, as well.