9mm AR problems...

[walmart_ar15]

Bent buffer Retainer

Check to see if bolt/BCG is flush at the end of the upper receiver. If Ok, then check if when closing the upper receiver to lower, the buffer is being pushed back just slightly into the buffer tube.

If not flush at the end of upper receiver, then you have out of spec parts in the upper. Could be bolt/BCG, reciever, or the barrel installation.

If not pushing back the buffer when closing, then you have out of spec lower.

If above are ok, then check under side of Bolt/BCG. Does it have scratches? Also check the grove cut for the buffer retainer to ride in, does it have scratches? Then finally check the to see if the buffer retainer is "riding" in the grove cut for it. If any of above, likely you may have out of spec bolt/BCG, retainer, or receiver.

If lots of scratches in the grove, then your retainer is too high (out of spec), if scratches are outside the grove, then your Bolt/BCG maybe rotating inside the upper causing it to hit the retainer on return. Too high retainer can also cant your bolt face downward causing ftf issues. Your last shot stuck could be caused by the misalignment of the retainer with the bolt/BCG.

Just 0.02.

[Atlantaboi2012]

Why do people opt to do 9mm on a AR platform? I always thought that was a strange combination.

[Intimid8tor]

Why do people opt to do 9mm on a AR platform? I always thought that was a strange combination.

Because the are super fun and the platform remains the same.

[TZL]

Cheap plinking without going to 22


9mm can be found for $199/k

Also many indoor ranges don't allow 556/223, so I built a 9mm ar for bringing newbies to first time shooting events, everyone loves to try a real ar15, albeit a 9mm one

Why do people opt to do 9mm on a AR platform? I always thought that was a strange combination.

[Atlantaboi2012]

Cheap plinking without going to 22


9mm can be found for $199/k

Also many indoor ranges don't allow 556/223, so I built a 9mm ar for bringing newbies to first time shooting events, everyone loves to try a real ar15, albeit a 9mm one

Gotcha... it makes sense...I hate shooting .223 indoors. it defeats the purpose of the round that is meant for distance. yeah 9mm would be a good training round for indoors while maintaining the functionality of the AR platform

[Atlantaboi2012]

Cheap plinking without going to 22


9mm can be found for $199/k

Also many indoor ranges don't allow 556/223, so I built a 9mm ar for bringing newbies to first time shooting events, everyone loves to try a real ar15, albeit a 9mm one

Gotcha... it makes sense...I hate shooting .223 indoors. it defeats the purpose of the round that is meant for distance. yeah 9mm would be a good training round for indoors while maintaining the functionality of the AR platform

[Falstaff]

Hey OP, if you have the Promag plastic magwell adaptor, I betcha a new quality Spikes, rock river or Hahn may well solve your feeding problems...
I too fell for the Promag, there's a reason it's only $34... It's total crap, there's tons of info on arfcom about pustol caliber ars and the consensus there is that the Promag is useless. There are a few guys who report success with it but most say its junk. The consensus is now that the Spikes enhanced (adjustable)magwell adaptor is the best. I am using ASC and modded Uzi mags in mine w/no issues now.
To the person who asked "why a 9mm AR" I say it's more fun than a barrel of monkeys! Especially if you have plate racks/steel to shoot at and a good red dot sight, ping-ping-ping-ping! And 9mil is cheap still (relatively)..

I do not understand what your saying about the bolt/buffer issue. I do know that not all bolt catches work with 9mm setups, and not all 9mm mags have followers with the ability to lift the bolt catch after last round. Not to mention the fact that if you don't do something to slow that bolt down ( heavy buffers, spacers) it will break the bolt catch and possibly the receiver casting..)
The Yankee hill buffer is heavier and more importantly longer (the length restricts travel rearward to reduce subsequent forward inertia and stress on bolt catches) and its cheap. The new spikes one is also getting good reports, I haven't tried it.

My budget build setup:
YHM 9mm marked upper
Spikes 16" 9mm barrel
RRA magwell adaptor (at $175, the most expensive piece in whole assembly!)
Aero precision lower
CMMG ramped bolt
YHM 9mm buffer with std CAR spring
UTG carbine free float rail ( very impressed with this super cheap ~$40 rail)
CAA collapsible stock
Vortex strikefire red dot
I don't have the 9mil deflector/dust over and don't think I'll need it.


Promag magwell adaptor for sale: $16.00 shipped and its yours!!

[Intimid8tor]

Hey OP, if you have the Promag plastic magwell adaptor, I betcha a new quality Spikes, rock river or Hahn may well solve your feeding problems...
I too fell for the Promag, there's a reason it's only $34... It's total crap, there's tons of info on arfcom about pustol caliber ars and the consensus there is that the Promag is useless. There are a few guys who report success with it but most say its junk. The consensus is now that the Spikes enhanced (adjustable)magwell adaptor is the best. I am using ASC and modded Uzi mags in mine w/no issues now.
To the person who asked "why a 9mm AR" I say it's more fun than a barrel of monkeys! Especially if you have plate racks/steel to shoot at and a good red dot sight, ping-ping-ping-ping! And 9mil is cheap still (relatively)..

I do not understand what your saying about the bolt/buffer issue. I do know that not all bolt catches work with 9mm setups, and not all 9mm mags have followers with the ability to lift the bolt catch after last round. Not to mention the fact that if you don't do something to slow that bolt down ( heavy buffers, spacers) it will break the bolt catch and possibly the receiver casting..)
The Yankee hill buffer is heavier and more importantly longer (the length restricts travel rearward to reduce subsequent forward inertia and stress on bolt catches) and its cheap. The new spikes one is also getting good reports, I haven't tried it.

My budget build setup:
YHM 9mm marked upper
Spikes 16" 9mm barrel
Aero precision lower
CMMG ramped bolt
YHM 9mm buffer with std CAR spring
UTG carbine free float rail ( very impressed with this super cheap ~$40 rail)
CAA collapsible stock
Vortex strikefire red dot
I don't have the 9mil deflector/dust over and don't think I'll need it.


Promag magwell adaptor for sale: $16.00 shipped and its yours!!

He's using a dedicated CMMG lower.

[Falstaff]

Oh duhhh, reading comprehension fail.

[mike_c70]

Paid Riflegear a visit this morning. Spoke to a young gentleman behind the counter (sorry I didn't ask for your name). First thing he said that ProMag is garbage. Unfortunately, they couldn't find the metalform 10/20 they had in stock so I'll give them a call. He did recommend to try out the ASC magazines since he hasn't seen any failures with it.

Anyways, he brought one out and cycled a few snap caps through the gun. Sure neough after the 3rd snap cap, it FTEd. We noticed that the magazine follower had a huge gauge in it, like someone took a chisel to it. This is getting troublesome now.

I'm going to give JSE a call tomorrow and see if they can do something about it. The gent at Riflegear said that if I was willing to leave it with them, they could try and diagnose the problem further and try and fix it (at a price of course). This is outstanding service!

[crazychinaman]

Hi guys,

Finally got a chance to shoot my recently built 9mm AR. Ran great when it ran. The problems where the following:

1) Buffer won't bounce back after last round (bolt open). I would have to complete separate the upper from the lower to get the buffer to spring back. Can't figure out if it's catching on the buffer catch pin. It's a 9mm Heavy buffer. Thinking of switching it out with a ST2 to see if it makes a difference.

2) Got a bunch of FTFs and FTEs. It looks like the bullet is jammed hard into place, there's a pretty significant dent in the top of the bullet. RO says 99% mag issues. I'm using ProMag 10 rounders which I've heard where hit or miss. Any other available 10 rounders. Might as well built a DDLES glock lower now if it doesn't fix the problem.

Other than sorting these two big issues, it was awesome to shoot. Felt like shooting my buddies 15-22.

Oh yeah, lower is a CMMG dedicated with a JSE upper and CMMG bolt if that helps any with diagnosing the issue.

Help is much appreciated.

where are you located.I could look at it and you borrow some mags form me.I have c/p mags and uzi and promags mags.Mine work fine in my 9mm.I use a asa 9mm adapter on a asa upper .Pre ban lower.I use heavy buffers with 9mm PLus P loads.

[mike_c70]

where are you located.I could look at it and you borrow some mags form me.I have c/p mags and uzi and promags mags.Mine work fine in my 9mm.I use a asa 9mm adapter on a asa upper .Pre ban lower.I use heavy buffers with 9mm PLus P loads.

Appreciate the help. I'm in Carson. PM incoming.

[MUSIBIKE]

I have made up 4, 9mm AR15s out of various lowers, trigger groups, rear stock assemblies and so forth. The buffer is a consideration with 9mm. It needs to be heavier.
The feed ramp you have is a bit suspicious? Is your mag well adapter sitting high enough on the lower?