Review: CMMG .22lr conversion for AR-15

[nutz4utwo]

A few weeks ago, I purchased a CMMG .22lr conversion for my AR-15. Overall, I have enjoyed shooting it and I happy I bought it. I recommend it with reservation due to issues from a chipped extractor (see post #2). I think this type of simple .22lr conversion is one of the greatest strengths of the AR platform. What other rifle can be so easily and cheaply converted to a plinking trainer? Sorry if this is long winded, it is what I like to see in a review:

I ordered it from:
CMMG 22-CONV 22LR Conversion Kit for AR15 with 26 Round Magazine

$185 plus about $10 for shipping

Ambient weather was excellent to deal with, they billed me correctly, and shipped it out quickly via UPS. Kit includes the .22lr conversion bolt, a plastic tube to store it in, one 26 round Black Dog magazine, and basic instruction sheet.



You unload the rifle, pull the rear take down pin, and pull out the .223 bolt. Then slide in the .22lr conversion bolt and that is it. It operates as a .22 blowback action using your existing barrel and trigger components. The 22.conversion also has a short 2 inch smooth bore “barrel” that slides into the .223 chamber to extend it and make it so you can fire .22lr. You can see it in the photos- it looks like a .223 cartridge but is steel.



The overall operation and design of the bolt is just like a Ruger 10/22.



Bolt hold open after the mag is empty is accomplished by the extra tall red magazine follower. The mag follower sticks way up and the bolt runs into it and stays open. Not the best way of doing it, but it is adequate. When you pull the magazine, the bolt will close. I needed a yellow range flag to keep the action open for cease fires. The normal AR-15 bolt catch does nothing with this kit.



Magazine: Very sturdy. Easy to open via small hex screws. The plastic mag body has brass inserts so the screws don’t strip the threads. No feeding issues yet. It is difficult to put all 27 rounds in the magazine. I can only get about 22 in before it gets really stiff. This is the place that builds them:

Atchisson/Ciener© 27 Round Full Body 2nd Generation Smoke Magazine

Accuracy: Good, but not great. Shooting off sandbags at 50 yards, I usually get 8-10 inch groups of 10 shots. This is from a LMT Defender M-4 with 16 inch chrome 1/7 twist barrel, iron sights. I am not a masterful precision rifle shooter, but for comparison sake it shoots a little more poorly them my scoped 10/22 (5 inch; 10 shot groups at 50 yards from rest) It more then meets the purpose of cheap training and plinking.

Ammo: Have only had a chance to run Federal Wal-Mart 36 grain bulk and Winchester 40 grain Wildcat through it. CMMG recommends Federal 40 grain high velocity ammo.

Functioning has been near flawless with the Winchester Wildcat. I did have one Winchester Wildcat fail to ignite due to primer issues. The firing pin stuck the case and gave it a serious dent, but it failed to ignite. I blame the ammo.

Federal 36 grain bulk works well, but not flawlessly. With over 500 rounds, I have had 5 short strokes where the bolt fails to cock the hammer properly. When shooting this Federal 36 grain, I can hear louder and softer firing and smack of the bullet in the backstop. I will stick to 40 grain, reasonable quality ammo and I think it will work well enough for every day use.

My rifle has very stiff hammer and disconnect springs. It might not have any cocking issues if a lighter spring set was installed. If I continue to have short stroke issues, I will consider modifying the bolt’s recoil spring or…?

There were some extraction issues as well see post #2.

Cleanliness: Not as bad as I thought. There is a lot of .22lr crud that gathers in the receiver. It is sort of gritty large particles. It cleans out quite easily. The barrel gets that crud in it too. I have been pulling a bore snake through it before firing .223. The instructions recommend firing a few .223 to clean out the gas system every few hundred rounds.

There you have it. Hope someone finds this useful.

[nutz4utwo]

Extractor: When the kit was new, I threw in some .22lr action proving dummies. To my surprise, they failed to extract properly. I took the kit to the range and it extracted fine for a few hundred rounds. It would not, however extract a live round from the chamber without firing it. The extractor did not get a good bite on the cartridge rim.



I took it home and disassembled it. Upon close inspection, I noticed the extractor was ever so slightly chipped. Also, the recess cut into the barrel was a little shallow so when the bolt closed all the way, the extractor was pulled away from making strong contact with the cartridge rim. This is not good considering this is a new piece of gear.



I considered calling CMMG and complaining, but figured it was not worth the hassle. I opened it up and punched out the extractor roll pin. I then using my bench grinder and files to carefully reshaped the extractor. I also had to grind a small bit from the surface where it contacts the bolt so that the now-smaller extractor would sit in the correct place.



Also, I took a file to the barrel extractor recess and shaved off just a bit so the extractor could bite the cartridge rim easily.



I deburred the rails while I had it apart too. All in all it took about an hour. It was a pain on a new piece of equipment, but easier then dealing with warranty or ordering parts. If you are less mechanically adept then I, Black Dog Machine sells extractors and firing pins too.

http://blackdogmachinellc.net/ciener-extractor.aspx

Extraction and ejection has been flawless with the reground extractor.

[dnowell]

Great writeup! I just got one of these but the AR that it's supposed to go with hasn't arrived yet, so I haven't had a chance to test it out. I've read about Aguila SSS 60 grain 22LR performing better in these kits because it's designed for 1/9 twist rate, whereas the lighter 40 grain rounds like 1/16 twist. If you have a chance to fire any I'd love to hear whether it's more accurate.

Also great pictures - must have a nice camera.

[EAJ]

Thanks for taking the time to put together a thorough review. I've been thinking about the cost of a conversion vs. purchasing the SIG 522 rifle they're coming out with this summer. )

[Ridgeline]

As has been said "Great Review" and thanks, I belive you have answered my concerns and will be ordered too. Also let us know about the 60 grain if you test before we do...once again Thanks!!!

[nutz4utwo]

Great writeup! I just got one of these but the AR that it's supposed to go with hasn't arrived yet, so I haven't had a chance to test it out. I've read about Aguila SSS 60 grain 22LR performing better in these kits because it's designed for 1/9 twist rate, whereas the lighter 40 grain rounds like 1/16 twist. If you have a chance to fire any I'd love to hear whether it's more accurate.

Also great pictures - must have a nice camera.

I will try to get my hands on some of the 60 grain Agulia for testing. I see Cabela's has them, but they are $50 for 500!!! Ouch!

Cabela's -- Aguila .22 LR Sniper Subsonic 60-gr. Ammunition with Dry Box
I have not seen any key-hole-ing or other evidence of an poorly stabilized bullet in my 100 yard targets. One day, if someone has a chronograph at the range, I will ask if we can run a few rounds through it to get some speeds. I have a 16 inch chrome lined 1/7 twist barrel.

As I said earlier, accurate enough.
My real concern is if this thing is going to have any long term reliability ejection or short stroke/cocking issues. Only time will tell.

[nutz4utwo]

Ammo update:

So I went to Cabela's yesterday and bought various .22lr and made it to the range this morning. I am mostly interested to see how reliably they cycle the gun so I shot 100 rounds each (except only 10 shots for the 60 grain Agulia $$$), but I will post accuracy as well (all shot from 25 yards, from sandbags, LMT Defender M-4, 1/7, with CMMG .22lr conversion, iron sights)

Winchester Wildcat: 40 grain. 2 failures to fire! There were heavy dents in the cartridge rim, but no ignition. No cycling or ejection issues. 3 inches for 10 shot group.

Federal Bulk from Walmart (red box): 36 grain. Muzzle report and recoil noticeably different from round to round. 3 short stroke issues where the hammer was not cocked. I would fire, hear and feel a reduced recoil and not be able to fire again. Looking into the ejection port, I could see the hammer resting against the bolt. I couldn't put the safety on as the hammer was not cocked. No ejection or failure to fire issues. 3 inch 10 shot group.

Federal Bulk from Cabela's (Champion, blue box): 36 grain, but slightly higher velocity then the Red box Federal Bulk. Report and recoil were much more consistent and there were no FTF, no ejection, and no cocking issues. 2 inch 10 shot group.

Remington 22 Thunderbolt: 40 grain bullet. These had the strongest and most consistent recoil/report of any of the rounds. No FTF, no ejection issues, no short-stroking issues. 2 inch 10 shot group.

Aguila: 60 grain monster .22lr round! These things are ugly and no one at the range had ever seen one. They have a .22 short cartridge with a monster bullet on it. I only fired 10 rounds, but there were no failure to fire, no ejection issues, no short stroking issues. They seemed to run the gun just fine. Point of impact was about an inch lower then the high velocity rounds (at 25 yards). After firing 10 rounds, I had to stop because the smoke it produced really irritated my eyes. I was wearing safety glasses, but there was acrid smelling smoke coming out. I wonder what sort of powder they put in them. It was not pleasant. Due to this and their high cost (10 cents each) I will probably not buy any more. 1.5 inch 10 shot group.

Another thing to note: I occasionally get my face lightly "peppered" by crud in the receiver and gasses escaping. No big deal, but keep them goggles on!

I don't know if my iron sight shooting is good enough to tell the difference between these rounds so take everything with a grain of salt. They are all accurate enough for my plinking purposes. My favorite is the Remingon 22 Thunderbolt and then the Federal Bulk Champion blue box. I will stick to those for now.

[Chuck R.]

Thanks for the very timely report, I’ve just ordered a Spike’s Tactical conversion for my LE6920 with 1:7. The Spikes is like the CMMG, but with nickel plating and “O” rings on the chamber insert.

I’ve been reading everything I can on ammo selection, and your tests are pretty much consistent with what I’ve read. The conversions can be finicky, but you will find ammo it likes.

Chuck

[ksokie]

Just FYI. From the few reports I've read about these CNMG kits on the interenet, make sure you check the steel 223 casing on the end of the conversion kit for cracks. I've seen pictures where the cracks run the length of the 223 sized casing.
Thanks for the good reveiw. I've been really tempted to purchase one of these. It would go along good with my Advantage Arms conversion for my G19. Might actually be able to afford to shoot a few hundred rounds at a range session.

[dnowell]

I know I'm getting into this thread a bit late, but -- thanks for running the ammo through. I'm still waiting on my rifle, so can't test my kit out yet. Good to hear about the strange smoke on the Aguila 60 grain stuff. I had thought about ordering a pile of it but at that cost and with this review I'll stick to the normal stuff. Also thanks for the warning to wear glasses!

[dukalmighty]

I bought one years ago,I also bought a friend a full auto conversion you can see my wife firing on the M16 thread I posted,JSE Parts has the Magazines a little cheaper than retail price and I bought several for around 28.00 for the 27 rounder full body mags,the Black dog mags also have spring and follower replacements which is great since the OEM metal magazines don't seem to be disassembled.The AR15 barrel is just a smooch larger .224 than the 22LR bullet so it doesn't get the accuracy like you would get in a dedicated 22 upper.
Most of the time the"SMOKE"is caused by bullet lube,I know when I was using tumble lube bullets,the lube coating caused a puff of smoke everytime I shot

[nikdfish]

I recently picked up a CMMG conversion myself for use with a 16" chrome lined 1:9 HBAR upper, and picked up a brick of Aguila 60 grain subsonic LR to go with it. I will admit the fumes can sting the eyes if there's not a breeze, but the improved accuracy is worth it. I was using glass at a bit over 25 yards, but was standing and leaning against the car a bit since I didn't have a bench. I think that the 60 grain would have single ragged hole potential if it was shot from a bench (I'm getting older & a bit wobbly as I don't get out shooting much these days). The following has 36 grain in the lower two targets & 60 grain in the upper two, 20 rounds on each target except for the upper left which has 10 (and a bit more left windage added in). Firing sequence was counter clockwise starting at the lower left and firing at a rate of one every 2-3 seconds.





Nick

[GreenHorn]

Sidenote: Remington Thunderbolt is notorious for fouling up your barrel. 200 rounds completly clogged my 22 walther. I could not get a brush through it or even the weighted end of a bore snake.

Local gunshops around here refuse to sell it. You can only get it at Dick's and Walmart around here.

[Reborn]

I bought one of the CMMG conversions and dropped it in over the weekend. Fun to shoot but I had several fail to fire. The weapon would fire fine and than a click. I would have to remove the mag. Recock the weapon and reload the mag. The weapon would then fire and work for several rounds. A couple of the the rounds that didn't go off I pulled the bullet and couldn't even see a mark from the firing pin. The extractor wouldn't pull the unfired round. I had to slip my knife blade under the edge. The testing of this conversion was done is my Olympic Arms rifle. I will be contacting the manufactor this week. Oh and one other thing......I could feel unburnt powder or something stinging my cheek on a few rounds. I will be switching the kit to my DPMS rifle next weekend. Sure is a lot cheaper to shoot. Grouping was about 3 to 4 inches at 60 feet.

[ccman]

Reborn.

Try different ammo.