Home Forums Hunting & Shooting AR and Tactical Rifles 9mm upper swap?

Is there an option out there for a swap and shoot 9mm upper that will work on a standard AR15 lower with no alterations? I understand that the proper magazine adapter or mag insert would be needed.

CMMG makes a good 9mm upper, and they sell a stock PMAG 9mm adapter insert for a stock AR lower - no mag well insert required.

https://cmmg.com/adapter-magazine-9-ar-conversion-10-30rd-2-pack

You-Tube shows the conversion running, I haven't tried it - but I do have a CMMG pistol upper that runs great on a dedicated 9mm lower for Glock mags.

I like the radial blowback design, seems to be reliable so far, and an easy way to dump money at the range...

I have wondered about this as well, what about buffer and springs, do they have to be changed out for the conversion to run?

CMMG recommends the rifle buffer and spring, I think the current experience is better using an H-2.

I've got a CMMG 16 inch barrel and radial BCG to put together - bought it after watching the reviews online, and the right deal popped - haven't assembled it yet.

For the 9mm pistol with the CMMG barrel and radial BCG - I had to use a rifle buffer and spring as recommended by CMMG - in the brace.

Thanks for the info.
I bought a Spikes Tactical 9mm and like it a lot but it has a total different style buffer and spring that are on a guide rod, kind of like a JP Enterprises style.
I was thinking about converting over another AR to 9 but was not sure about the buffer and what had to be done.
As was posted above, I know a new upper and something would have to be done about the mag well but not sure what else.

Quick question, do you prefer the mag adapters like are listed or just the insert that drops into the receiver?
I would think the receiver block might be a better choice as I already have Glock mags. That way I would not pick up the wrong 5.56 mag by mistake, but I don't know.

I have not personally shot the PMAG adapters - I watched some on-line reviews, read some more, and decided to try it.

If you want to stick with Glock magazines - it's either a dedicated receiver, or an insert - all will work, but expect to have to do a little tweaking with gas, buffers, magazines, and / or ammo with any of these systems.

For a dedicated lower - CMMG's bolt carrier is not slotted for the stock pistol caliber ejector for 9mm, you delete the ejector from your lower with their BCG and barrel.

I wanted a generic rifle lower to work - so went with the PMAG inserts - they were also quite a bit cheaper at one point than 33 round Glock sticks.

I'll either paint the PMAG body, or swap out a base plate - CMMG sells marked PMAGs, but they are expensive.

Why a 9mm rifle? - for me, simple caliber, mild recoil for young / new shooters, another way to shoot without being tied to an ammo shortage in one caliber, and I've got surplus Glock mags.

This is where I start getting lost. I don't have a lot of knowledge on AR's, so when the topic turns to different buffers and springs, I quickly start getting lost. Is it safe to assume that the H-2 is a different weight than a standard rifle buffer and spring? Also, are these 9mm uppers blowback and do they house their own ejector?

One thing I remember from the 9mm days is they are hard on hammers. The RR NM will not hold up as well as others so it'd pay to check with the MFG. if you have an aftermarket trigger.

Ok,

I’m not the expert - just another tinker with the platform.

Majority of 9mm are blowback - probably 99%, with the cartridge housed in the bolt / carrier - it’s one unit with the cartridge seat milled into the face of the carrier. The carrier is slotted for a static ejector that is fixed into the lower or mag well adaptor - it’s the dog leg looking piece in the left of the lower - looking from the rear.

There is no separate “bolt” as with the stock AR - the carrier becomes the “bolt” but you’ll see the terms interchanged. The 9mm one piece is typically heavier than a stock BCG - it’s a solid piece of steel.

CMMG designed a “radial delayed blowback” bolt with a matching barrel extension. The bolt and carrier look stock, but the assembly is spring loaded and pinned together - and there is no slot for the ejector - the bolt has an ejector in it. If you put the CMMG upper on a 9mm lower, the fixed ejector has to be removed - typically just knocking out a roll pin.

Basically- the radial cuts on the bolt lugs and matching barrel extension cause the carrier to move to unlock the bolt, so the blowback pulse is somewhat lesser than a straight blowback pulse.

Neither recoil is bad - it’s a 9mm, but it’s typically more than you’d expect in a small pistol cartridge in a rifle. I’d compare the difference to carbine and rifle length gas tubes - the recoil from both is mild, but the rifle length is typically slightly less.

Buffers - Stock is no marks, and you go up from there - H1, H2,H3 - you can Google the weights - I can’t remember them off of the cuff. If you’re over gassed (edited) in a direct impingement rifle, a heavier buffer may slow the carrier down enough to balance the system.

If you’re a shotgunner, it’s similar to switching your gas gun between field and trap loads.

No dealings with a gas operated 9mm AR but the Colt type uses a dedicated 9mm buffer that weighs about as much as the H3 maybe a little more. I’ve used them on an over gassed 223 WSSM and 25 WSSM.

Just mentioned the hammer aspect cause no one runs a stock trigger anymore it seems.

Special 9 mm buffer and standard carbine spring will work. ATI actually makes a pretty nice adapter to use Glock magazines. Add an upper of your choice and you should be good to go. Make sure your trigger is PCC rated which means pistol caliber carbine.
I've looked at going this route but personally I would recommend dedicated lower.
The above recommendation is with the idea of the bolt carrier is included with the upper .

Thank you for the info.

For no alterations to standard AR lower, look at the mean arms endomag. Basically you take a 30 rd Pmag, strip guts out and install emdomag guts. Shazam done
https://www.meanarms.com/products/detail/endomag-9mm

Thanks for all your responses, guys. I appreciate it.

I would agree that a dedicated lower is best. As I recall not all hammers will work with the 9mm "bolt." I shoot PCC's (9mm AR-15's) regularly in matches and have for years. They're fun and cheap to shoot. In the last few years a lot of people have gone to the SIG's which are a gas design, not blowback. They have much less recoil than the blowback design with the very heavy bolt/carrier.