CMMG Pattern Dedicated 22 LR Reliability

I am curious about experiences with dedicated CMMG pattern builds. Mine took a little tweaking to get it where I want it, but it has always eaten about any ammo I load in it.

I bought a few thousand rounds of "tarnished" factory second ammo cheap before the pandemic and its pretty crappy. 2 of my sons and I were shooting 22 LR today - Ruger MKII, Marlin model 60 and Walther P22 all choked hard on the factory seconds. Not the dedicated rimfire AR, it ran through it without a stutter.

That has been a pattern with the gun, it just runs and runs. I am using RTB (CMMG) and Black Dog mags, extra power extractor spring, and a bolt weight but it was as reliable without the springs and weight.

I am very interested to know if I just got lucky, or if the CMMG pattern runs well for other folks.

Andy

I’ve put together two CMMG style dedicated ARs. They’ve been as reliable as you can expect for a 22lr.

My first was Spikes Tactical setup way before CMMG started making 22lr stuff. The design is the same. The 2nd was using the RTB parts and a Beyer’s sleeved barrel.

Both run great with blackdog mags. The RTB works great with smith mp22/15 mags and the catch22 spacers. The spikes gun is having some problems with those, but hopefully I can figure that out.


Sent from my iPhone using Tapatalk

They generally run about as good as a semi .22 can.

Like any other semi .22 they can dislike a load. Mine chokes on a load that my AA Glock probably runs best on.

I think there are an awful lot of .22s that seem unreliable or inaccurate because present-day ammo quality is pretty bad.

I don't think I ever had stoppages growing up. As an adult, I've bought standard and bulk 22 that had upwards of 10% (or more) duds.

Dedicated CMMG rifles seem pretty good. Atchison and Ceiner-type drop-in units are only "Meh" because of the long faux chamber free-bore jump.

Do you consider the bolt weight a worthwhile upgrade?

The stock CMMG setup bounces pretty badly, which makes the marginal extractor worse.

Quote:

---

Originally Posted by AndyLate

That has been a pattern with the gun, it just runs and runs. I am using RTB (CMMG) and Black Dog mags, extra power extractor spring, and a bolt weight but it was as reliable without the springs and weight.

Andy

---

Yes, I think the bolt weight is worthwhile and it definitely runs cleaner.

I agree the extractor is pretty weak. I have the Bore buddy extra power springs and extracting an unfired round is still 50/50 at best.

I would be happy to send you my weight to try in your build.

I am on my third bolt weight - the first was brass and broke at the front "bridge". Bore Buddy replaced it with a stainless weight that cracked at the same spot. They replaced that one as well and I haven't broken the third one.

I also had consistent doubling with the standard velocity ammo, bolt weight, stock mil-spec style trigger, and loaded 25 rd mags. Swapping in a polished and plated trigger and reduced power hammer spring set resolved that issue.

Andy

P.S. The stainless weight breaking is not common, I think it was a tolerance stacking issue. The brass weights were gorgeous but brittle.

I use the bore buddy adjustable weight kit.

https://borebuddy.com/product/22lr-bolt-weight/

The stainless inserts work great for me. I tried the tungsten but it was inconsistent (dead trigger every so often). Too heavy for the ammo I was using. I have the Tacom3g firing pin and extractor and the bore buddy extra power extractor spring.

I use the Hiperfire competition trigger. It hits very hard which minimizes light primer strikes with 22lr, which I found is most of your problem. Not to mention the trigger is very nice. No take-up. Small and positive reset.
https://www.hiperfire.com/product/hi...h-competition/

I use S&W mags with the redimag adapter which I modified with a Dremel to cut out the mag catch so I can use the better Catch 22 mag catch. It's about as reliable as a 22 semi will get.

Quote:

---

Originally Posted by Adrenaline_6

I use the Hiperfire competition trigger. It hits very hard which minimizes light primer strikes with 22lr, which I found is most of your problem. Not to mention the trigger is very nice. No take-up. Small and positive reset.
https://www.hiperfire.com/product/hi...h-competition/

---

Its interesting that some folks have an issue with light strikes/misfires and some with a too-stout hammer drop. You and I are a good example but the web shows neither of our guns is an outlier.

My gun was destroying FP springs, basically on every outing. It was also doubling on a full 25 round mag, and this was repeatable under specific conditions. I installed a semi-generic polished/plated GI trigger set (Brownells ?) with reduced power hammer and trigger springs and both issues were solved. It has an ok trigger for a plinker.

I run the standard/solid BB weight with SV and HV rounds. I don't remember having light strike/failure to fire issues at any point - it is notably more reliable than any other (edit - rimfire) semi-auto I own.

The only issue mine has is extracting unfired cases - IMHO the CMMG pattern extractor is sub-optimal, even with the strongest BB spring. The easy fix is to just pull the trigger and the case comes right out :)

Andy

I did slightly reshape the front of my extractor where it was contacting the grove in the barrel. This lets it sit all the way down on the rim.

Yes, there seems to be some general interference between the extractor and groove.

We had a dedicated barrel where the groove was clocked a bit wrong and the extractor would contact the side.

With that fixed, the bottom of the groove does seem to lift the extractor slightly.

The stock extractor also seems to be pretty soft.

Perhaps the BoreBuddy hardened extractor is an improvement.

Quote:

---

Originally Posted by Todd.K

I did slightly reshape the front of my extractor where it was contacting the grove in the barrel. This lets it sit all the way down on the rim.

---

Quote:

---

Originally Posted by AndyLate

Its interesting that some folks have an issue with light strikes/misfires and some with a too-stout hammer drop. You and I are a good example but the web shows neither of our guns is an outlier.

My gun was destroying FP springs, basically on every outing. It was also doubling on a full 25 round mag, and this was repeatable under specific conditions. I installed a semi-generic polished/plated GI trigger set (Brownells ?) with reduced power hammer and trigger springs and both issues were solved. It has an ok trigger for a plinker.

I run the standard/solid BB weight with SV and HV rounds. I don't remember having light strike/failure to fire issues at any point - it is notably more reliable than any other semi-auto I own.

The only issue mine has is extracting unfired cases - IMHO the CMMG pattern extractor is sub-optimal, even with the strongest BB spring. The easy fix is to just pull the trigger and the case comes right out :)

Andy

---

That's what's great about the Hiperfire. The cam design allows more primer strike force while lightening the pull weight. I have the medium springs in and it is very light (never measured it). The heavy ones would make it lighter, but due to lower receiver tolerances, the slightly thicker heavy springs drag on the lower a little. I could fix it with a dremel touch touch up, but the trigger is light enough and the strikes are heavy enough. Yes, I found my CMMG firing pin spring totally destroyed when I changed it out with the bore buddy one. It was broken in half, but somehow still worked semi reliably. I have run a bunch of ammo with no issues. I even used the cheap Winchester copper plated hollow points in action steel with very few mishaps. Most guys stay away from Hollow points in action steel.

It looked to me, the tacom3g extractor was slightly better than the bore buddy. No measuring or science behind it. It looks to reach a little deeper and is sharper.

Clint would be better suited to look at the differences better than I.

It is working great for me though.

https://taccom3g.com/product/extreme-extractor-ar-22/

Just an update - still shooting my 16" CMMG pattern dedicated rimfire AR with CMMG and Black Dog mags. It's still amazingly reliable and incredibly fun to shoot. I hit the range today with 2 of my sons and as usual some folks had to come check it out. It just runs and runs and my boys (ok, 30 something men) were hammering 50 yard steel plates as fast as they could squeeze the trigger.

I am guessing I am well over 10K rounds, the firing pin return spring breakage went away, and I am happier with it every time I shoot it!

Andy

I should have included this in my update. My third Bore Buddy weight also broke at the bridge. BB would have replaced it, but I just filed and polished the break and continue to use #3. Now I wish I kept my broken brass weight :)

I say my polished and plated "GI" trigger with reduced power hammer spring is "OK" because it has so much takeup/smooth creep that it almost feels like a short 2 stage trigger with a very light second stage. It is smooth and acceptably light though.

Andy