I’ve been tinkering with the idea of building a short .22 AR pistol. I’ve got a brace kit, stripped lower and LPK, CMMG conversion kit and a bunch of mags.

Today, I bought a random assortment of AR parts from a local guy for cheap. Included were a slick side flattop upper and a 4” lightweight FF rail. These would be perfect for the .22 pistol build.

Does anyone know if the CMMG 4.5” barrel will work with the 4” rail? Will it require something like a mini flash can to extend past the end of the rail?

I’ve also got a couple of suppressors will probably use on occasion.

I can’t say for sure but rimfire barrels usually sit about 1.5” deeper into the upper receiver.   Compare the length of a CMMG 16” rimfire barrel to a 16” centerfire barrel and the rimfire barrel measures closer to a 14.5” centerfire AR-15 AR-15.

Maybe someone else will chime in or measure their 4.5” CMMG upper.

Yes a 4" rail will work and YES you will need something like the Kak Micro Flash Can to clear the handguard. I'm in the process of finishing up a pistol with the CMMG 4.5" barrel. I'm just waiting on my handguard w/barrel nut and Kak flash can to finish. Here is a picture. As you can see the barrel only sticks out from the receiver 3 1/4"

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If you use a 7” hand guard you can use a 5.5” CAR flash hider and the flash hider slots will be just past the handguard.
You can then replace the flash hider with a rimfire can...

It will be almost dead even with a 4” rail Attached File

If you have suppressors to run on it I'd go with a longer rail to give you a better place to grab the gun.



My setup. I have the gemtech quad lug adapter on it to get the can off easier although if you shoot a brick through it the qd setup will get carbon locked. Mine gets run on my m16 lower often and I just use a mallet to break up the carbon and get it off.

One thing I'd do if I did it again is go quad rail. Tried to run a front grip(not an issue on a pistol) and it ended up hitting the suppressor mount.

Thanks for the info and pictures. I'd rather not have the muzzle inside the hand guard. I've dealt with trying to get a stuck suppressor thread mount off in that configuration before and once was enough for me.


Does anyone make a 6" .22 barrel? They seem to jump from 4.5 to 9 from what I can find.

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I solved this problem with the Gemtech QDA attachment.

My Mask didn't stick out enough from a 7in rail on a 4in bbl.  I also had the issue of the rear endcap sticking sometimes.  Either required removal of the rail to get at the can for cleaning.  The QDA turns it into a 3 lug style like an HK (Its actually a 4 lug design but works the same way) for easy peasy on and off and bumps the can a bit further out front so you can actually grab it without needing to remove the rail.  When the Mask is on another host I put the QDA on a dummy inert tube for just in case as a safey mechanism.  Should the upper need to be fired I don't have to worry about someone's hands being in front of the muzzle.

The QDA option is a bit expensive but a workable solution that IMO was worth every penny for my situation.  YMMV.

OP, as far as the jump in bbl length sub 5inches will keep the bulk pack high velocity stuff subsonic.  I blow through those 1400 rnd Remington buckets via the binary trigger and my setup alot.  The only way I can afford to do so.  I think the jump to 9 inches is simply the fact that 7 inch rails are a extremely common AR15 handguard length.  Anything shorter is usually wandering into niche territory. A 9 inch AR22 bbl will let you comfortably use a 7 inch rail and the can not being recessed.  The AR22 barrels recess back about 1.5 inches into the receiver.  If you still want quiet you can use standard velocity or match ammo in addition to the "subsonic" labeled loads but it will cost you a bit more per shot fired when compared to the bulk stuff. A 6 to 7 inch bbl that still tucks into a common carbine length handguard and  lets high velocity go super sonic makes no sense at least from a manufacturing point of view. Might as well go uber short to stay subsonic and deal with the recessed muzzle or a super short handguard or jump to 9 inches.  Even if they did offer an in between size it probably wouldn't sell to well. Just my 2 cents.  YMMV.  

Same with mine. I ended up using the dremel to shorten the mlok screw.  It can get tricky to install the VFG back on but it's doable and solid when done successfully.

I went with the griffin checkmate QD on the end of my CMMG 4.5" barrel.  I think their current 22lr can uses a standard 3-lug adapter, too.  If you cant go with a dedicated can, this is the next best thing.  Going to a slightly longer handguard gives you a lot more and a lot cheaper options.  The money you save on buying the longer the handguard pretty much covers the QD for the silencer.

A little off topic, but if you're building your first dedicated .22, don't ignore the charging handle.  Save yourself the headaches and either get a charging handle for a .22 or take an old one and fill it about 3/4 of the way with JB Weld or something.  When you have a misfeed due to bumping the magazine or for whatever reason, the casings like to get stuck in the charging handle and it is a PITA.

This is especially true if you're going to be using the conversion unit with the 5.56 case looking spacer on it.  That blows gas through the back of the receiver from the gas tube.

MAS defense has three different lengths of "slim" flash cans....perhaps the short or medium will work for you:
https://www.masdefense.com/1-2-x-28-TPI-s/136.htm

I have the medium length on their 5.5 inch hand guard.

FYI; was also about to grind down the mlok hardware screws, but a couple of #10 lock washers inside the vertical grip did the trick.
It left just about 1mm between the mlock hardware and flash can.  

That's what I do too

CMMG upper

Another vote for the Gemtech QDA solution since you run suppressors. I have one and you can buy additional mounts for about 30$ for quick hk style swapping
https://www.gemtech.com/22-qda-thread-mount-threaded-1-2x28.html

Here is a couple of pictures of my pistol with a CMMG 4.5" barrel and Guntec 4" handguard. I used a Kak Micro Slimline Flach Can which is 1.750" long and it just clears the end of the handguard by 5/16".

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Here’s mine with 4.5 barrel and 7.5 hand guard.

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And then with the suppressor. Well the fake place holder since I’m lazy and the real one is on another rifle right now.

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With a 4” hand guard you’ll need something about 1.5” long to get outside the hand guard

A 1.5" long flash can will barely clear the end of the 4" handguard. The Kak Micro sticks out 5/16" from the end of a Guntec 4" handguard. See my pictures above. With a 4.5" barrel and 4" handguard, I would go with a flash can that is at least 1.75" long

cmmg 4.5" with tri-lug, under a guntech handguard