So I bought a Lothar-Walther barrel to build a dedicated .22 upper around.  The problem is, I ignored this statement on their website:

"This dedicated 22LR barrel has a .675 long breech and will not work with a newer style .700 long breech collar."

https://www.lothar-walther.com/rimfire/945/ar15-carb.-l.-life-hd-coated.22lr-mud-1/2-28-unef-2a-l-16.50-cr-moly-steel?c=24


Sure enough my new build won't fire and won't extract.  There's the smallest gap, probably right at 0.025", between the face of the WL barrel and the feed ramp of the CMMG collar.  I contacted CMMG, they said they don't have any of the older style collars laying around.

So does anyone have suggestions?  I saw references to Walthar-Lother barrels for .22 builds on this site as recently as 2018 and 2019 with no comment about requiring an obsolete breech collar.

Call or email them.  They are aware that CMMG changed this dimension.  If you are stuck with the barrel, I think CMMG will sell you a collar with that "older" dimension.  Otherwise some have had luck sanding down the backside of the collar to match the barrel 'stub' dimension.  But I'd start with a LW, they are making barrels with the 0.700" dimension now.

I've contacted CMMG.  They say they don't have any of the older collars.  I might reach out to LW, but they very clearly state "No Returns" and this is my fault for not measuring the collar I had before ordering.

I have a buddy that's agreed to mill down collar if need be.  I'm trying to avoid that route though, I'm not sure what that does since it'd change the location of the detent pin.

I just bought a barrel from them and  emailed them if the CMMG collar would work.
They replied as long as it has a .675" long breech collar, it will work.  I don't have a bcg yet so I assumed it would.
Never heard of 2 different lengths. Tried searching but didn't find anything on collar lengths.  So I don't think they know what the CMMG colllar length is.

Same thing happened to me.  Once I spoke with L-W and found out the proper dimension of the collar, I measured mine found it was too long, and reduced it.  I used a piece of 120 grit sandpaper laying flat on my work bench.  I sanded, measure, sanded, measured, rinse repeat until I got to about .678.  I then took some 220 grit paper and sanded and measured the rest of the way to .675".  My new dedicated .22 upper runs like a sewing machine using all ammo including subsonic.  

For what it's worth, I bought and used the Bore Buddy SS weight and pressure plug.  The plug works as advertised.  The weight works great for keeping the rifle clean.
I'm not sure how it works but after shooting 400 rounds of .22LR in this rifle, I was prepared for a lot powder residue and crud.  When I got the rifle home and took it down to clean it, I was surprised at how clean it was. The BCG had very little build up and the trigger group was fairly clean.  I have a Spike's dedicated upper that gets full of crud, especially in the trigger area.  This rifle had some powder residue there, but nothing like I've been used to.  I don't know about the other claims but keeping the rifle clean is one that does happen.
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Did you remove the material from the side that goes into the barrel then?  I was originally planning on doing that, but then then realized the spring detent pin would be about 0.075" off and I thought it might cause problems.  I've got the collar with a buddy right now who's going to take it to his dad's shop and mill down the face on the feed ramp side instead to .675".

What's .025 amongst friends?



I did.  It works.

My collars are so tight on the LW barrel nub that I don't believe the detent matters.

Good work- I missed this.  You did the right side.  The rest is all about recoil spring.

L-W has been aware of the dimension change since September of last year when I alerted them to it.  They ran some custom 17hm2 barrels for a group of us on another forum, and it caused a lot of head scratching until we realized a dimension had changed. I had both lengths of collars floating around in my different bolts, so depending on which bolt was grabbed, the upper would run or not run.  

Sanding/milling/otherwise removing material from the collar does not change the detent location relative to the barrel, since the material is removed from the opposite side from the feed ramp.  Cut without fear!