has anyone tried different barrel extensions so it fits in the upper tighter?

in other words,   i want my barrel to fit super snug in upper.   what is easiest way to do that?   i am trying to increase accuracy in my "precision" ar build.   currently an fairly standard aero upper with a jp super match barrel, geissele handguard, lmt enhanced bolt.

it seems like the tighter it is , the better accuracy i should get assuming i am trying to go from 8's and 9's to 4's or 5's

just trying to rule out some simple fixes.

Read over the tacked thread “hellbenders guide”. You’ll want to shim the barrel with SS shim stock or use the loctite method to increase the contact between the receiver/barrel extension.

Edit: I’ve had good luck with some regular forged uppers, but I’d recommend a Vltor MUR-1a or a quality billet upper for a heavy barrel. Thicker walled receivers are believed to help with the overall precision of the system.

This, or the BCM uppers as they are under sized for a very very tight fit. I used loctite on all mine. but not needed with BCM uppers. Disregard if going billet

You can find thick walled billet uppers on sale at JSE Surplus. They're discontinued MEGA uppers, even though theyre no longer labeled as MEGA. I have one and the extension fits very tight

I use bearing sleeve retainer compound.

If it's only a little loose Loctite 609 or 620 will work well

Stainless steel shim stock is available in a wide variety of thicknesses.

On one truly sloppy upper (7.62x39mm) I used Devcon steel epoxy knowing I would never take it apart.

Millions of AR's have been built without going to these measures that shoot very very well.

I’ve been using BCM uppers on my last several precision oriented builds. I don’t know how much it helps, but it certainly doesn’t seem to hurt.