I bought a CMMG 22 stainless steel conversion kit for my M&P Sport and it was delivered on Tuesday. I finally got to hit the range this evening and try it out. It is great, worked without any problems except for one mag. The mag that came with the conversion is gray and the two extra mags I bought are black (add said they are made by CMMG).

On the back of each of the black mags there is a small 1/4 long plastic bump on each side of the spine. The gray mag doesn't have these bumps and the dimensions are the same for both style mags. The gray mag holds the bolt open after the last round and the two black mags didn't until I ground off the bumps.

I only did one black mag to start with, didn't want to screw up two mags if my theory was wrong! (Who, me wrong, neveeeeeeeer!) The black mag with the bump still on it jammed in the mag well of the rifle. I had to open the rifle and give the front edge of the mag a couple of good whacks with a screw driver handle to dislodge it. The other black mag without the bump worked just fine. So when I got home tonight I got the dreaded Dremel out and ground off the two bumps on the last black mag. Works just fine in the rifle now.

I was shooting CCI MINI MAGS and they shot very well at 25 yrds. I also had some Winchester Wildcat ammo that was the pits. It didn't shoot groups as much as a shotgun pattern.

Here are the last two groups I shot with the CCI ammo. These were shot standing with support under the hand guard. I am very please with the conversion and it was a cost effective way to do more shooting at less cost. I can't afford a dedicated upper at this time so the conversion was my only option. While not a tack driver, it's just fine for paper punching or plicking. I highly recommend it.

This is the 1st target group:



This is the 2nd target group:

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gunfighter48
NRA Life Member

So I'm a little confused; did the gray mag work? Or did it give you fits?

The grey mag worked just fine from the start and it was the one that came with the conversion unit. The two black mags were the extra ones that I bought. Once I trimmed off the bumps (tabs) on the rear of each mag they worked 100% also. They also hold the bolt open after the last round just like the grey mag. So everything works fine now.

The thing I don't know is if the bumps (tabs) on the back of the black mags would cause them to jam in other ARs. But my guess is that if they didn't jam they probably won't hold the bolt open after the last shot. The tabs on the back of the mags keeps them from seating far enough into the mag well so the hold open will work. So some trimming on them may be necessary even on other ARs. But it's an easy 4 minute fix with a Dremel or file.

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gunfighter48
NRA Life Member

Are you using the CMMG .22 barrel also, or the .223 barrel?

I'm using it in my 556 barreled M&P 15 Sport. The conversion shoots more accurately than I was led to believe by the internet gun commandos!!

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gunfighter48
NRA Life Member

I have had one for a year or so now. Thousands of rounds thru it. No problems at all. I got 2 gray mags with mine. I use the Federal bulk packs thru it. Mine is in my M&P Tactical, using the factory barrel.

A recommendation; .22lr is not the best stuff to run down the 5.56 barrel because of the gas tube. 22debris and junk will start loading up in there. The pressures developed by the 22lr are plenty to cycle the action as retrofitted, but the gas tube collects material as it is now defunct.

You are good to shoot it, a LOT. But before you put many many rounds thru it, remember every once in a while to clean out the gas tube. It's not the easiest cleaning job in the world, but can be done and will need to be done with some regularity when you throw 22's down the AR barrel.

The result of build up is slow cycling when shooting .223/ 5.56 ammo, or failure to extract as reliably.
When you can, find a used receiver and get a dedicated .22 barrel from CMMG. Make a .22 upper, and minimize the issues you would otherwise eventually have to wrestle with.

I am talking 1000's of 22 rounds before issues, so it's not like you will shoot it once and the gun goes KaPutz on you. Just info to remember. Have FUN!!!!

And it will lead up the barrel, so make sure to clean it thoroughly.
Accuracy is not bad with a regular AR barrel, good enough for plinking, but .22s do work best out of a lighter twist rate like 1 in 16.
I have one as well, it may not be a varminter, but it's good enough for what I want.

I just bought a SW MP15 Sport 556. Haven't even gotten to shoot it yet but I was looking into the 22 conversion kits for it. I have read several reviews regarding CMMG being a reliable brand. Is this true and if so what am I better off going for. The full upper conversion kit or just the bolt conversion kit? There isn't a great price difference and as far as reliability I would prefer the better.

If the goal is inexpensive practice sessions using .22lr, why buy a whole .22lr upper when you can buy a complete 15-22?

The 15-22 can not be converted to shoot 5.56. The lower can not be adapted to a 5.56 upper. Getting a dedicated 22 upper on a real 5.56 lower gives you the strength, durability and the options of swapping calibers quickly and easily.
Plink for an hour with 22lr, then in less than 1 minute, switch to a 20" FF upper with an optic already on it, and start wicking targets at 600 yards.

At 600 yards, the 22lr is going to get there, but you will be aiming about 17ft high to hit the target, and about 3 feet into the wind.....................

I bought the conversion kit because I wanted cheaper practice with my Sport lower which has a $209.00 Timney trigger assembly in it. I can buy 500 rds of CCI MINI MAGS locally for about $34.00. And the MINI MAGS work great in it.

I will be trying some other cheaper brands of 22 as I get time and money. It lets me get some much needed trigger practice in. It's been 15 years since I've had a rifle to shoot. So far the conversion kit has been absolutely reliable with good ammo. From what I've read the Remington Golden bullets work well in it but I haven't tried them yet. The black magazines with the green followers have been absolutely reliable and I now have 4 of them. I also have the gray mag (with a green follower) that came with the conversion and it's also been 100% reliable so far.

I would've liked to buy a CMMG 22 upper but just didn't have the money at this time. So the conversion was the next best thing and I've very pleased with it.

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gunfighter48
NRA Life Member

Yeah my gun shop had a special on the mp15 sport which is why I spent the 200 dollars more to have a gun that is more fun to shoot compared to buying the 14-22 which is more resticted. I still keep my options open to swap out the upper or bolt to shoot 22. I guess ultimately I am more interested in seeing if the cmmg is a reliable brand or are there better brands out there more affordable. I heard you can do just the bolt conversion for 22 but I saw only for 100 dollars more I can get a whole other upper dedicated to the 22. I appreciate those who have replied already. I'm new to the assault rifle world as well as this forum. Your feedback is much appreciated. Thanks joe

I shoot the 15-22. I get the urge to shoot .223/5.56. I put down the 15-22 & pick up the 15-Sport. Takes about 2 seconds.

*EDIT*

My periodic cranial-anal inversion condition reared it's ugly head. I didn't process the fact you had a scope mounted on your 5.56 upper. A separate upper makes sense because you don't have to buy two scopes to get in practice, or spend time swapping on/off a scope and having to re-zero it.

My bad. I apologize.

Ok. Now I completely understand. I'd do the same if I had a Timney Trigger in my 15-Sport.

Reading the review on this at Cheaperthandirt one person notes the intention of the bugs is to accommodate different guns. If your gun doesn't need them then they're meant to be filed off, at least according to that.

Thanks for the "review" of it. If you don't mind me asking, where did you order it from and what was the total shipped price you paid?

I think I might get one of these just so I can spend more time at the range without the ammo cost of the .223 being so much.

How is the long term reliability with this kit? Any long term damage to the barrel?

Is the twist rate ideal for .22??

Basically I can't decide if I want to get this, or a dedicated .22 upper.


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For the money, you'd be better off getting a dedicated .22 AR, like the S&W M&P15-22, or even building a dedicated upper.

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*Aim small, miss small...

I bought the conversion kit from Dillon Precision. The conversion kit with one mag was $149.95 and bought 2 extra 25 round mags for 35.98. I don't remember what the shipping was.

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gunfighter48
NRA Life Member