CMMG .22lr conversion - a brief review

[lindertw]

I spent a bit of time googling for spare parts for the Atchisson-Ciener/CMMG .22lr conversion. In addition to finding someone that offers spare recoil & firing pin springs (here), I found a few interesting links for troubleshooting the unit.

I had a little bit of free time, and I love to tinker, so I decided to strip it down and give it a good cleaning and see what the innards look like. There's a thread on TOS that shows how to field strip the conversion unit for cleaning.

After reading this thread I decided to venture into the firing pin and clean up that area. After driving out the FP retaining pin, I had to work pretty hard to get the FP out. I figured maybe it was pretty gunky, but after cleaning up the channel with a q-tip and wiping down the FP I inserted it to see if it traveled freely. Oddly enough it did not; there was a lot of binding.

I grabbed a small strip of 600 grit paper and soaked it with oil, wrapped it around the FP and gently turned it. Every few turns I would insert it into the bolt to see if it dropped free. After a few minutes I massaged the FP so that it rides freely in the bolt.

I wonder if the FP not moving freely in the bolt may have caused some of the failure-to-fire issues that crept up with different brands of ammo. I'm going to run the various ammo again at my next range visit to see if any changes are noted. Additionally, I may try clipping one coil from the FP spring to see if that further alleviates light primer strikes.

I found one small burr on my extractor and I plan to remove it from the bolt and then clean up any rough spots - maybe that'll reduce extraction issues that creep up... I'll post further updates as I continue to get this thing tuned.

[Logic]

It seems that most people running 22 uppers or conversion kits are using some form of high vel ammo such as federal bulk or the similar. Anyone using standard vel ammo reliably both in semi and full? What about sub-sonics?

[Littlelebowski]

LittleLebowski was also there, but he was with someone on the line so I chose not to interrupt/introduce myself...

Say Hi next time! I would have loved to see the .22 conversion.

[lindertw]

Say Hi next time! I would have loved to see the .22 conversion.

will do!

[lindertw]

another update:

I removed the extractor today and filed down that small bump/burr on the end. I left the firing pin out and reassembled it to see how it extracted during hand cycling and it seemed kind of weak. I'm curious if that small bump on the end of the hook was all that was grabbing the brass... I hope to get some range time in the next day or two to see how it runs.

Either way, I plan to replace the extractor with a BDM piece.

And in the FWIW department, I found that a BCM extractor insert fits in the extractor spring on the .22lr kit. I may experiment with the black/blue inserts to see if they have any benefit with extraction as there are no apparent sources of heavy duty extractor springs.

I'll post more updates as I plow ahead

[lindertw]

I was able to hit the range today after work, and my firing pin mod did the trick. I fired ~100 rounds, a mix of Fed Bulk, Aquila and Win Bulk with 100% success!

I compared the firing pin mark on the brass and the indentation was more apparent. Weird to think that the FP was hanging up in stock form. If you're having failure to fire problems you owe it to yourself to check the FP to verify it moves freely in the channel. I forgot to note that my Colt 6920 (as modded by SAW) has a low mass hammer and 'blue' hammer spring (trigger pull weight is ~4.5#).

My extractor mod was on the money too - not one failure to extract. It's nice when it feeds/fires/ejects like it should I still plan to experiment with blue/black extractor spring inserts to see if it helps or not.

I'll throw some pics up ~Friday to show what I modded - maybe it'll help others.

[MX5]

Since people are now buying .22 LR conversions as fast as they can find them, lets add some clarity to the issue of .22 LR ammo & malfunctions. I've been shooting various conversions for a good number of years & have tested a lot of .22 LR dedicated weapons, conversions & suppressors.

Essentially, expect each individual .22 LR firearm or conversion to "like' or 'dislike' various types & brands of ammo. Some will feed, fire & eject everything while others are very picky as to which ammo they'll digest. This is common within the .22 LR world & similar weapons & conversions lined-up side by side might, or might not, function with the same ammo. The real bitch is when you get one that will only fire one brand & type of ammo. Either stock-up on that ammo or dump the bitch.

Many people spend a lot of money on quality ammo for their centerfire weapons, but when they shoot .22 rimfire, they go for the cheapest bulk ammo available. The trick, if there is one, is to try as many different types & brands of .22 ammo to find out what works best in your gun for accuracy & function. Then, stock-up on it accordingly. Typically, better quality ammo = better performance = higher cost. But, the cost of the .22 conversion & ammo is so much cheaper than the centerfire version, it doesn't pay to go cheap here.

CCI Mini-Mags usually will work in just about anything. They're very reliable & accurate as .22s go. However, I once had several examples of a very nice .22 autoloading pistol to test & one of them would only work with CCI Green Label. I mean, nothing else would function reliably for one magazine - only this brand & type. Generally Ruger 10/22s, Ruger Mk series & Walther P22s work well with lots of different ammo - suppressed or unsuppressed. But, there are examples out there that don't work for crap. Sometimes it's the weapon, the ammo or the shooter.

Advantage Arms conversions come with a list of recommended ammo that usually works best. My personal Glock conversion works best with their recommendation, especially when suppressed. However, I've tried it with other ammo & found that it works fairly well to a point with ammo they don't recommend. It gets dirty faster with the 'non-specified' ammo, & suppressed it will work for short periods of time until it gets too dirty to function properly.

Find what works best for you in your weapon & try as many different types ammo as you can. They're really very cheap & it's well worth it in the end. If it functions fine with Wally World Special Bulk Ammo - so be it! Treat each one individually & find out what shoots best in your example. Then, have at it.

[dtibbals]

I have been thinking about getting one of these as well just for the fun factor. I "think" I read somewhere that these kits can create problems with LMT lowers. I think it was something about the hammer breaking or something similar to that. I could put it in my Colt LE6920 but was a bit worried when I heard about parts breaking in lowers.

Anyone else heard about this? Seems that I read it here or on AR15.

[lindertw]

my BDM extractor arrived in the mail today:

BDM on the left, factory on the right






I should have taken a pic before I filed on the factory extractor - it had a noticeable bump on the extractor face, which I'm certain caused the FTEs I had initially. After the file/cleanup job it worked like a champ, but the BDM piece looks like it'll perform well.

I have not tried it (yet), but the black insert from a BCM AR15 extractor upgrade fits in the .22lr extractor spring. If you're having extraction problems and have one on hand you could give it a try, otherwise order the BDM replacement extractor.


I oiled up 600 grit sandpaper and turned the FP down a little at a time until it fell in/out of the FP tunnel smoothly (it was very rough and would not fall free in factory trim). I think this alone solved the light primer/failure to go bang that I initially experience with Remington and Aguila ammo. I've read that you can trim 1-2 coils off the FP spring (not shown), but I don't intend to go that route as all the ammo I've tried now fires without issue.

Note how ugly the feed ramp is - that's how it came from the factory At any rate, it feeds fine so I'll leave it be...


That's about it for now. I hope to hit the range tonight/tomorrow and see how the new extractor performs.

ETA: I just got back from the NRA range (it was packed) and I was able to put ~100 rounds down range to function check the new extractor. It fed/fired/ejected with zero issues - ammo was a mix of Fed AE 5022, Aguila, Remington bulk pack and Fed bulk pack.

[Bimmer]

Hey Linder,

I'm the OP, and I really appreciate this. This is a better response than I could have ever hoped for.

Now, back to writing letters to Santa about how good I've been...

Bimmer