LW barrels are compatible with the CMMG bolt system and the old, shallower collars.

I know you posted in the other thread; maybe I'm misunderstanding your question. I think the BCG and barrel would work in any standard AR upper.

My first LW 22lr barrel was an extremely tight interference fit into an Anderson upper. I thought that tightness may have contributed to the accuracy. I now have a 10.5 inch LW barrel that I tossed into a receiver for testing; it is not an interference fit and has maybe 20 ft lbs of torque on the barrel nut because I didn't have access to a vise. It's also quite accurate.

Maybe that interference fit isn't as important as I thought.

 

I think you'd be better off building it piece by piece using an Anderson upper and any CMMG/RTB 22lr bolt and handguard of your choice.

A word of warning -- the last 3 RTB uppers I have purchased (all during the '20/'21 gun buying frenzy) had issues on assembly and required shims to be added between the upper and barrel shoulder. One would not even run when used with a centerfire, had to be pulled down and replaced with an Anderson. Could I do those 3 uppers again, I'd buy Anderson for all three, I've always had great luck with those.

As always, YMMV. Were you one of the original Lothar-Walther group buy participants? If I could do the barrel buy over, I would have opted for a 14.5" (with a pinned and welded muzzle device) to help with the swollen case issue. I'm in contact with another gentleman who just had a 14.375" made by Beyer, so it'll be interesting to see how his works out in that regard.

 

I think you'd be better off building it piece by piece using an Anderson upper and any CMMG/RTB 22lr bolt and handguard of your choice.

I don't want to sound like an Anderson commercial, but I've assembled some number of uppers and lowers using Anderson sport lightweight uppers (no forward assist or dust cover) and closed trigger guard lowers. They were typically $40 per upper or lower when I bought.

Anderson is widely derided in AR-land as the choice of poverty, but I never found anything out of spec*, they always had a good lower to upper fit, and function has never been a problem. *(The lowers do take a shorter pistol grip bolt, so I just cut the end off a regular bolt.) They are forged 7075.

I just bought a billet lower because it has a screw keeping the bolt catch in place rather than a spring pin, and closed guard Anderson lowers aren't to be found. It was three times as expensive even though billet is weaker than forged, it has a bunch of little sharp edges the Andersons don't, and the fit to the upper is looser.

 

What about Rock River? Do they use standard AR barrels?

 

To the degree there is a single standard format in 22lr ARs, it's CMMG. That's why LW made their barrel to work with the CMMG system.

Rock River looks like a great bolt and barrel, but you aren't going to be able to drop an LW barrel and Rock River BCG into an upper and have it work.

 

I've not had any problems with Anderson or Palmetto State Armory upper or lower receivers. Most of my builds are one or the other.

I'm interested to see if the shorter barrel helps with the 17m2 or not.

 

I've had very good luck with Aero Precision uppers and lowers, and that is what I used for my AR22 build with a CMMG bolt and a LW barrel. I see no reason why Aero parts would not work just as well with a 17HM2 barrel. The nice thing about the Aero Precision lowers is they have a nylon tipped set screw accessible through the pistol grip well that can be adjusted to take the slop out of the upper to lower fit. All it takes is a long T-handled 1/8' ball end hex wrench for a rock solid fit.