I need a 9mm AR SBR.

[usmcvet]

I'd love to see photos of your build.


Sent from my iPhone using Tapatalk

[Muzap]

I had to mess around with buffers and springs. The A5 with a rifle spring worked well and so does the Spikes Heavy Buffer with an extra heavy Wolf carbine length spring. I think the A5 was more affordable.

I purchased a DDD Glock receiver before they went under and QC10 picked up the design. After the stamp came back, QC10 was going and was already putting out improvements like the bolt I wound up using.
I used the LWRC UCIW stock with a Heavybuffers.com buffer/spring. And of course a Geissele SSA trigger.
The upper was built with a RRA 9mm receiver and a QC10 9mm bolt, with a TROS 5" 3-lug barrel.
Oh, and an Octane 9 can with a Griffin 3-lug adapter.
The QC10 bolt/carrier actually has its own removable weight. So, you can play around both with buffer weight/spring, and removal/re-installation of the carrier weight.
The LRBHO actually worked, but after snapping the bolt catch, I decided I was better off without that feature. After replacing the bolt catch, BHO did not work and I have not made the adjustment necessary to revive it.
It took some work to get running right, but was well worth it:

[AlphaTango23]

I have a PSA billet lower and Spinta Billet Upper/ BCG, with a KAK Shockwave.

5,000 round with ONE, just one failure to extract. Running Glock 33 round mags. The most fun I've ever had.

[Dannybot]

Nice! Do you have an issue getting enough buffer weight with that shorty stock?

I am not that impressed with the need for more buffer weight. I have a dedicated Colt pattern Spikes lower and a Rock River mag well adapter. I have tried a variety of combinations:AR 15 and AR 10 carbine springs, JP bolt, NFA bolt, travel spacers, and buffers weighing from 0.95 oz up to 5.3 oz.

My ultimate set up is a carbine buffer with the JP bolt and AR15 carbine spring without a spacer in a Spikes 9mm lower (which came with an extended bolt catch, so no need for spacer). This gives me reasonable split times and reduced bolt bounce. I am using 115gr hand loads for this combo loaded a little on the light side, but 147 gr factory ammo shoots equally soft.

[mkmckinley]

THis probably isn't news to anyone but the theoretical benefit of a heavy buffer is to delay extraction for as long as possible. This should result in less blowback and gas venting into the receiver, less receiver noise in suppressed applications, less chance of a ruptured case, more time for the bullet stack to rise in the mag, and less stress on the hammer pin in the receiver with corresponding reduced chance of egging out the hammer pin hole in the receiver compared to a lighter recoil assembly. Recoil assembly should include all the mass that the round has to drive back to cycle the action which on a 9mm AR is the bolt, buffer, spring, and to some extent the hammer. I'm no engineer, but according to this guy's calculations a recoil assembly weight of 1.75-2.15 lbs is ideal for 9mm. This guy also supports an ideal buffer weight of about 1.75 lbs for a blowback 9mm.

Data point: I had a custom buffer made so run 9mm in my Vltor A5 receiver extension. It's a stainless steel buffer that's about 3/4" longer than an A5 buffer. It has room inside for 5 buffer weights and I'm using 5 tungsten weights. The buffer weighs 12.6 oz and the QC10 boltis an additional 15.3 oz. With the spring that's a total of 1lb 14oz (1.875lbs). That recoil assembly ran 100% today with a Hahn dedicated magwel, 8" Faxon barrel, QC10 upper receiver, and LMT 2 stage trigger. Ejection was extremely consistent and lockback was 100% with Palmetto State Armory mags. The internals were surprisingly clean for a blowback and there was no gas-to-face even with a standard charging handle. Ammo was NATO spec ball and standard pressure 124gr reloads. Of note: the Wilson Combat TTU trigger I tried would not reset with the 9mm parts. Next I will test this thing with a suppressor when I can find a 1/2-36 HK 3-lug adapter.

I really think Colt mags are the way to go with 9mm AR pattern PCCs. If I'm treating this thing as a training adjunct to my "real" 5.56 AR then I want to be running ~30rd mags. "Good" Metalform-manufactured 32rd Colt pattern mags mags are actually cheaper than 33 round Glock mags and they're made of thick steel. I do have a bunch of Glock pistol mags but I don't think I'd be using 15 or 17rd Glock pistol mags much anyway since hand placement would have to be different than the beer can grip I'm used to using on an AR mag when I insert it. Also, if I was putting in a lot of reps with a Glock mag lower I'd be concerned that the angle you have to insert Glock mags would screw up my standard AR mag load. Finally, from asking around, it doesn't seem like anyone's fully worked out the kinks on the Glock lowers especially WRT lockback. Just my .02.

[Rayrevolver]

BLUF: Gonna see if I can make a AR-10 Rifle Buffer work as a PCC Buffer in a A5 RE.

I am in the process of building a "cheap" PCC to run in USPSA. If they would allow Pistols with Braces then I would have used something I already own (and its too short to SBR in Maryland, so its a brace or nothing). Hence the "cheap" part as this is a fun only thing, and the parts are adding up. I also need a 1/2x36 3 lug!

With respect to the above post, I also run exclusively with the Vltor A5 system and this PCC will need to run on the system. My initial plan was to use an A5H4 and a spacer but after doing some research I need more buffer weight.

My options are a 10oz KAK buffer for $50, but then would need a spacer or 2 to makeup the up the extra A5 tube space. I pinged Mark about his custom buffer but that adds too much cost. What I did find out was that an AR-10 rifle buffer is longer than the A5 and shorter than a AR-15 rifle buffer. The specs say its 5.2" long and it looks like the bumper on the back is 0.5". That means if I can cut down that bumper I could get very close to a 4.75-4.8" buffer with the ability to run 5 weights.

So that is my plan. $12 DPMS AR-10 buffer from MidwayUSA and the spare tungsten weights I bought when I was messing with A5 buffers.

[Clint]

My options are a 10oz KAK buffer for $50, but then would need a spacer or 2 to makeup the up the extra A5 tube space. I pinged Mark about his custom buffer but that adds too much cost. What I did find out was that an AR-10 rifle buffer is longer than the A5 and shorter than a AR-15 rifle buffer. The specs say its 5.2" long and it looks like the bumper on the back is 0.5". That means if I can cut down that bumper I could get very close to a 4.75-4.8" buffer with the ability to run 5 weights.

So that is my plan. $12 DPMS AR-10 buffer from MidwayUSA and the spare tungsten weights I bought when I was messing with A5 buffers.

The 10oz KAK buffer is probably the easiest and best choice, but for a project, another option is to cut down the body of an AR15 rifle buffer.

This would leave the bumper intact.

[nate89]

I have a 16" QC10 gun that just runs. I have had issues in the past with other 9mm ARs, but this one is just as reliable as my 5.56 BCM. I went QC10 for the barrel, upper, lower, and bolt. A friend of mine had two out of battery detonations with his QC gun, and on using feeler gauges found out that the hammer would still pop primers when it was slightly out of battery. He ended up selling the bolt and getting a KAW valley bolt that does not have the same problem.

[Rayrevolver]

The 10oz KAK buffer is probably the easiest and best choice, but for a project, another option is to cut down the body of an AR15 rifle buffer.

This would leave the bumper intact.

Thanks Clint. There isn't a whole lot of room in the AR-10 buffer for 5 weights (when I cut it to A5+.75") and it looks like I will be at 10oz or so. If I take out most of the rubber spacers I buy more room, but I have not figured out if that means I can fit 6 weights. Probably not, but I should be able to use the full bumper.

This effort has turned into a big project. I had issues with the Spikes magwell adapter but Spikes CS squared me away. And then they offered me a deal on a dedicated 9mm lower (Colt). I have never dealt with Spikes and they have been fantastic, just wanted to give them credit.

I can only get 10rd mags, so I ordered some from ASC. And the bolt hits the feed lips! FML. So now I need to figure out that mess but hopefully get some Colt mags when I head into Virginia next time.

Its been an adventure and I still am nowhere close to firing a round. Even with the new lower, my overall cost is still low-ish.

Did Euro ever build or buy one???

[TomMontana]

I really think Colt mags are the way to go with 9mm AR pattern PCCs. If I'm treating this thing as a training adjunct to my "real" 5.56 AR then I want to be running ~30rd mags. "Good" Metalform-manufactured 32rd Colt pattern mags mags are actually cheaper than 33 round Glock mags and they're made of thick steel. I do have a bunch of Glock pistol mags but I don't think I'd be using 15 or 17rd Glock pistol mags much anyway since hand placement would have to be different than the beer can grip I'm used to using on an AR mag when I insert it. Also, if I was putting in a lot of reps with a Glock mag lower I'd be concerned that the angle you have to insert Glock mags would screw up my standard AR mag load. Finally, from asking around, it doesn't seem like anyone's fully worked out the kinks on the Glock lowers especially WRT lockback. Just my .02.

I agree and I might be coming around and preferring the Colt mags. I have both the CMMG (Colt) and NFA (Glock). That slight slant on with Glock mags always bothered me vs the straight Colt SMG mags. And if the Glock mag didn't have a plus 2 extension, the bottom of the mag angled up from back to front.