Seeking Input and info re 9mm AR build?

[Citadelgrad87]

I have a registered AR, it's a Bushmaster.

I am considering building/buying a 9mm upper for playing around with PCC, possibly in IDPA.

I have lots of Glock 32 rounders, and a bunch of AR mags/bodies, from Orlites to aluminum to Freedom week Pmags.

I know that there are a few ways to go, mag block vs mag inserts, but I never really rolled up my sleeves and did the homework. I know I'll need an upper but know NOTHING about them, and that I need to change the buffer but nothing specific.

What's it going to take to do this right?

[Sailormilan2]

I have a 9mm that I built on a standard lower that I use a Stern Defense insert on. That gives me the ability to go back to originality if I want to. I have the inserts for both the Glock mags and Beretta mags. Both work well. Though admittedly I have not yet tried the really large mags yet. This being CA and all.
The downside is that the Stern Defense adapters are kind of pricey, much more so than the Sylvan. But, I have read some comments about the Sylvan adapters is that there could be some fitment issues with Glock mags. So I went with Stern.
I have no idea which is actually “better”.

[Zenderfall]

I have two AR-9’s, one built up from a current AR-15 5.56 lower and another built up to take Glock mags using a dedicated 9mm lower.

There is no “right” way to do it, everything has tradeoffs in a 9mm AR platform.

there’s a video series on Youtube called Blowback9 that goes into a LOT of details about building and troubleshooting AR-9 builds.

but to get started:

if you want to use your Glock mags and your current AR-15 5.56 lowers, the only ways to go are either the Sylvan or Stern defense magwell adapters, and a glock-compatible upper (most are).

The Sylvan doesn’t have last-round bolt lock back ability. The Stern does, but it may be a little finicky. I don’t know how important that is to you, but it is a tricky design to make work considering glock magazines use the front part of the follower whereas the AR-15 system uses the rear part of the magazine well to catch the bolt. This is one of the reasons why the more reliable setups tend to be Colt magazine AR-9’s (lits of other details I dont want to get into)

both adapter relocate the mag eject button elsewhere. The silvan relocates to front of the magwell, the Stern has a button you press forward.

good luck with your build!

[george223]

I put an AR9 together a couple of years ago using a dedicated lower capable of using Glock mags. I wanted the classic Colt SMG carbine look (but with Glock mags). It took me awhile but I was able to find a 16" barrel with the A1/A2 front site. That wasn't easy to find. I also found a couple of flat top 9mm uppers, no brass deflector and no hole for a gas tube. I found one at APEX that was manufactured by Colt but it has pink camo on it and they called it 'Muddy Girl'. Oh well, ugly but functional. I bought the other off of Gunbroker. It had the same forging mark as the Colt but no stamp from Colt. I really wanted a carry handle upper but couldn't find one in my price range. I also managed to find a couple of Colt style gas deflectors and ejection covers. Normal AR uppers will work just fine if you don't care how it looks.

You can use a carbine spring but you need a heavy buffer that is 3/4" (if I remember correctly) longer than a carbine buffer due to the 9mm bolt being 3/4" shorter than an AR bolt carrier / bolt. Or you can use some sort of spacer. Some people use a stack of quarters. I bought a correct length buffer that was about 11 oz. The general consensus is that the combination of the buffer and the bolt should weigh 22-24 oz. I removed couple of the tungsten slugs from my buffer and replaced them with aluminum slugs that I just made from 1/2" AL rod.

When I took it out to the range, it ran fine at 1st but ran into some feeding issues. The 9mm round would strip off the the mag and hit below the chamber pushing the bullet into the case. Not acceptable. A quick search on Google found that a lot of people, but not all, seemed to have this issue with Glock fed AR9'. The fix is to grind a feed ramp below the chamber. I ended up buying a barrel from Taccom that has a ramp and no front site along with floating handguard. There isn't a lot of ramped barrels out there. Seems to work fine now but I have only taken it out once for a quick function check. The jury is still out.

I'm thinking of using my 2nd upper with a 9mm lower that can use the Colt / Uzi mags. The lower has a built in bullet guide. The availability of mags is an issue and is holding me back and at my age, do I really need another AR? Anyway, that's it in a nutshell.

[george223]

I'm curious if others have had feeding issues with their AR9 as I described in my previous post ^^^ and if so, what was your fix?

[Zenderfall]

Colt/Modified Uzi mag AR’s:

-more reliable than glock mags in an AR-9. The built-in guids in the magwell sleeve help to guide the rounds in better than how the Glock feed ramps work.

-the magazines are made of metal, and are double feed (like 5.56 mags) rather than single feed like the Glock mags. They’re also easier to load, not busting up thumbs or having to use a tool.

-the LRBHO works better because the magazines push up on the bolt catch in the back of the magazine rather than the front, like how Glock mags work, and therefore needing a “transfer” bar of some sort. Colt mags work so much better in regard to LRBHO.

-the magazines are found online and are about $15-$20 for a ten rounder. Made by Duramag, they are of excellent quality.

-ramped barrels are needed more for the glock mag AR’s than colt mag AR’s, as the round comes up at a steeper angle in those. The fix is…a barrel with a more “cut” out ramp in it, sadly.

-Is how Colt did it from the factory, Colt M635 (look it up) has been in service for decades and is basically an M-16 with a sleeve in the magwell. It’s a proven, reliable design that works really well.

-more people find the vertical mag looks “cooler” than the slightly angled Glock mags setup. I’m in that group.

the only advantage I can see from a glock mags AR, is that I have a bunch of Glock mags to begin with. If I didn’t already own a Glock, the colt mag AR is by far, superior in the reasons above.

[Sailormilan2]

You can use a carbine spring but you need a heavy buffer that is 3/4" (if I remember correctly) longer than a carbine buffer due to the 9mm bolt being 3/4" shorter than an AR bolt carrier / bolt. Or you can use some sort of spacer. Some people use a stack of quarters. I bought a correct length buffer that was about 11 oz. The general consensus is that the combination of the buffer and the bolt should weigh 22-24 oz.

I’ve seen two sets of numbers for the 9mm. 21.5oz - 23.5oz(from Colt), and the 22oz - 24oz already mentioned. With my build I started with 21.9oz(13.7oz(bolt) and 8.2oz(buffer)), and it seemed to work fine.
I recently tried a heavier buffer, just to see what would happen. I used an 11oz buffer (10.8oz by my scales). So, my total is now about 24.5oz.
With my reloads, jacketed bullets loaded to +P levels, the empties land about 4-5ft away. Lighter loads using lead bullets land about 1ft away.
So, for all around use I may need a slightly lighter buffer.

[Scotty]

I run a Stern Defense Glock mag adapter with ETS mag in IDPA. Works fine, no problems with the last round hold back. Used a 9mm buffer and spring. The only problems I've ever had was with the Mean Arms mag adapters. Lots of problems with the plastic ejector moving preventing the mag from going in or locking up an open bolt from closing.

[Oldluck]

Sounds like a fun build! If you’re using Glock mags, a mag block or dedicated Glock lower will work. You’ll need a 9mm blowback upper, 9mm BCG, barrel, and a heavier buffer (5.5oz+). Keep in mind hammer compatibility too. Tons of options — just depends how deep you want to go!