My 9mm AR15 mini rifle build

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someguy2800

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I recently got the hankering for something different than my hipoint 9mm carbine. The hi point was pretty accurate but it was picky on ammunition and you had to sight it back in after cleaning. I looked at other 9mm options but decided to just do a colt pattern 9mm AR15. I chose the colt mag pattern over a glock mag lower because they are more universal on parts and because I don't have a glock and I don't care for the looks of an ar15 with a glock mag sticking out of it.

Here is the parts list

BCA dual charging upper (I have not settled on what upper to use, I stole this one off my 223 varmint rifle to test)
PSA complete 9mm colt style lower ($180)
ADK 9mm bolt ($94)
kak pistol brace ($45)
Faxon 10.5" barrel ($112)
ebay 12" forend ($25)
slim krink brake ($20)
ASC 20rnd mag ($16)

Once I got all the parts I took the barrel off my 223 upper to test this out. My intention is to put a suppressor on this once I finally get mine through the paperwork so what I would like to do is get a bear creek side charging upper without the rear charging handle to put all this on to reduce the gas blowback around the charging handle. The bolt has a nice flat on the side that lines up nicely with the slot on my BCA upper so if i do that I will just drill and tap it for a side charging handle.

When I finally got all the parts and put it together immediately there was a problem. You could not engage the magazine with the upper attached. The magazine was hitting the inside of the upper receiver rails, the ejector, and the bolt. If you retracted the bolt you could smack the mag and get it to seat but if you released the bolt it would jam on the right feed lip of the mag and lock the gun up.

I ended up bending the ejector a bit to clear the left feed lip, bending the right feed lip up a bit and grinding it down slightly to clear the bolt, and I had to put the rear of the mag in the bench vice and squeeze it in about .020" to fit inside the upper receiver. Finally the bolt catch was too long and was sitting on the middle of the magazine follower instead of the stepped part on the back. So I had to take the bolt stop out of the lower and grind back the tip about .060".

With all that sorted I did a trigger job on it with the pretravel screw in the grip screw hole and went out to shoot.

Excuse the ridiculous huge scope, that just what was already on the upper. When I get another upper to use on this I will get a 3x prism scope or something more appropriate.

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So far it has functioned just fine with my 124gr FMJ handloads I shoot for action pistol. Here is the target at 30 yards sighting it in. You can see the low shots walking it up to the bullseye and then a 5 shot group.

The group above that I just shot one round onto the cardboard and then used that hole for the aiming point for the next 4 shots. I am happy so far with the accuracy. I will try it at longer range today.

I think it needs a bit more recoil spring and a rubber bumper or something inside the buffer tube. Bolt speed is a little violent.

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Another point to note for those deciding between a glock and colt lower, the colt style mag is very easy to load by hand. At least mine is.
 
I wonder if your mag issue is a universal problem, or if it is just a bad mag, or a stacking tolerances issue with your parts. I love the look, and functioning like that,it works, but I hate having to modify mags to work on ar pattern guns. Do you plan on picking up some more mags to try out? If so let us know how that goes too.
 
I wonder if your mag issue is a universal problem, or if it is just a bad mag, or a stacking tolerances issue with your parts. I love the look, and functioning like that,it works, but I hate having to modify mags to work on ar pattern guns. Do you plan on picking up some more mags to try out? If so let us know how that goes too.

I will probably get another 4 or 5 ACS 20 round mags. If I need to tweak all of them as well so be it.

I just shot this at 100 yards. This is the same load I shoot in my action pistol gun loaded with a 124 RMR FMJ. The wind was gusting pretty hard left to right so if this was in the calm I expect this would probably be a 3" round group

edit; oops here's the picture

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No pic of 100 yard group...and all the posts and pics of pistol caliber AR's really makes me want one. My brother got the CMMG 45 ACP and that thing is AWESOME.

If I get one I'll go your route and build myself. Nice looking "pistol" and Glad it shoots well for you.
 
Still haven’t gotten an upper for it but decided on flip up sights. I was looking at red dots but I don’t like batteries. These are UTG flip ups. They are okay. Tiny bit of front to back movement. No side to side movement.

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If you pistol buffer tube length is the same depth as a typical carbine tube depth... try a Tubbs flat wire .308 recoil spring.

I run one in my Colt Pattern 9MM PCC... MUCH less bark and blast. I also use a 7.5oz buffer weight... those two things dramatically changed the cyclic speed from Linda Blair like to Winnie the Pooh.

Best money I spent on my 9MM PCC.

Also try some Metalform mags... the Brownells ones are excellent.
 
If you pistol buffer tube length is the same depth as a typical carbine tube depth... try a Tubbs flat wire .308 recoil spring.

I run one in my Colt Pattern 9MM PCC... MUCH less bark and blast. I also use a 7.5oz buffer weight... those two things dramatically changed the cyclic speed from Linda Blair like to Winnie the Pooh.

Best money I spent on my 9MM PCC.

Also try some Metalform mags... the Brownells ones are excellent.

I think I will try the 308 spring. A pistol tube is the same length as a carbine. The buffer that came with it I think was 8 ounces on my scale. The cycle rate isn’t bad with my handloads but it’s a bit harsh with factory ammo.
 
Just wanted to update this. This darn thing has nearly run me out of 9mm ammo. Really fun to shoot at plates. Hits on a 8” plate standing offhand at 100 yards are easy. It shoots very comfortably with the light handloads I made for it (147 grain with 4.3 gr power pistol) but bolt speed and recoil is harsh with 115 grain factory ammo. Believe it or not the bolt hitting the back of the buffer tube will actually bruise your shoulder. I ordered a 308 recoil spring and a new frontier armory buffer tube snubber for it.

I have probably 500 rounds through it now without a single failure or hiccup. It’s feed fired and ejected everything I’ve put in it.

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Oh and it weighs 6.5 lbs with an empty mag if anyone was curious. I orderd a side charging upper for it as well so I will tap the bolt for a charging handle and swap the parts over when it comes. I’m a sucker for side chargers.
 
I finally got this together in its final configuration. I got a good deal on a bear creek side charging upper with no rear charging handle so I picked that up. I tore it apart and put my 223 barrel back on the dual charging upper, and put the 9mm barrel on the new side charger. For a charging handle I drilled and tapped the bolt to an M6 thread and made a charging handle for it. The handle is just a socket head cap screw with two nylon bushings glued on it.

I also got an extra power 308 recoil spring and a New frontier armory buffer tube spacer which the combination of those two tamed the bolt speed and recoil significantly. Its now very soft shooting.

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I made a spacer for my 9MM AR to help stop the issue of broken bolt catches. A long 9MM buffer will also stop the problem. Either way, it needs to be heavy.
 

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What weight buffer? It should be one intended for 9MM.

Its a solid 9mm buffer that came with the lower. I weighed it when I put it together and I believe it was 9 ounces. New frontier armory sells a buffer spacer just like you made. I think I paid like 7 bucks for it.
 
I was actually going to fashion a rubber bumper until I saw the new frontier one. Its not as soft as I thought it would be but it works.
 
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