9mm AR Reliability Help.... (Pics)

[JesseR]

I've exhausted my knowledge and internet searching. It's time to ask for help from my OSA family.

A year ago I purchased a 9mm AR from a member here on OSA. My understanding was the gun was used in 3 gun, reliable and good to go. Well I have not had the best luck with this gun. When I first took it out to the range with factory 115gn Fedral FMJ it would FTE while loading the next round every 4th or 5th round. Figured it needed hotter ammo, so I started reloading for the gun.

Reloads were hit and miss. I'd have the same FTE every 4 or 5 rounds. Upon reaching the max load data for TiteGroup, I decided maybe something else is the problem as the rounds are hot. *NOTE* I am not seeing any case damage at the current load. I do have brass discoloring from the AR but not from my Glock 17 or 26.

I was told the FCG was DPMS's, but I'm not sure.

Originally the gun had a HANN Top Loading Mag block installed. Upon inspecting, the ejector appears to be bent.

I do not believe it had a 9mm Heavy Buffer, however it did have a shorter spring then the rest of my rifle lowers.

The top buffer spring came in the gun, I've since changed to the lower buffer spring with RRA AR-15 take off buffer.

The gun came with a Ramped Bolt, but I don't know who made it.

So aside from the bent Hann Ejector and Buffer/Spring combo, All should be good. Too bad it isn't.

I decided I would start trying different know issue point to see if I could get it dump a full 33rd mag with out a problem.

First I replaced the buffer spring with the lower, longer spring. I then added a new unramped bolt and finally a new bottom loading adjustable mag block.

Results: nothing has changed for the good or the bad. The gun will still have times of great success with both factory and relaod as well as continual FTE's with both types of ammo. All of my Mags are C-Products, 20 & 33 with black and orange followers. Regardless I don't see any major change in the operation of the gun.

The only thing that provides 100% reliability is if I load just one round at a time in a Magazine. It will fire and eject each round every time. Put two rounds and I have a 50-50 chance of it ejecting the first round and loading the 2 round.

Go with 5 or more rounds and it is hit and miss for success.

So, what do to next? I built my neighbors 9mm AR with a RRA lower, RRA 2-stage trigger, Unramped Bolt and bottom loading Magwell mag block. His gun is 100% reliable... aside from the Trigger, mine should be too!

I humbly submit my problem for your help and suggestions!

--Jesse

 

[Rob72]

Hmmm. Without seeing or shooting your rifle:
How's your chamber? Clean/dirty? Have you thouroughly cleaned it with something like Kroil (or Marvel Mystery Oil)& JB Bore Bright?

Extractor look okay? How's rim engagement? If it is "snug" after being freshly cleaned, it may be too tight to engage after getting gunk on the breech face & under the claw.

You're saying it has trouble ejecting or extracting? It's a significant difference. If the fired case is not being pulled from the chamber, start with the above.

If the case is being pulled, but is then staying in the receiver (ie, not being ejected) then your issues revolve around drag & resistence, and/or ejector length(ie, it may be "short-stroking"). If this is what is happening, I would detail strip & thoroughly clean the weapon. High polish the ramp on the bolt, lightly chamfering the leading edge of the hammer recess (the sharp lip that drags over the hammer on recoil).

Also polish the hammer face & the feed ramp cuts. Examine the ejector for scoring on the sides, to make sure it isn't dragging on the bolt & examine your brass to make sure it is hitting on the lateral edge, not centrally.

 

[JesseR]

Rob, I'd like to thank you for the one and only suggestion to my problem!

Range Update

So I was able to visit the range this weekend and work with the 9mm AR... It was a positive experience and I was able to successfully put 200 rds of ammo down the pipe. This was factory WWB, Federal, Remmy, in addition to my special reloads. All few nicely and the gun ran very well.

What did I do?

1) Well I weighed all of my buffers and found one was about 3oz and the other was much heavier. I couldn't be sure since my scale can't go above 3oz. From internet searching I found a buffer spacer might be needed, and could only cost $1.75 in quarters put down the buffer tube. (http://suburbansdomain.blogspot.com/2010/06/175-solution-to-9mm-ar-15-problem.html)

2) Reviewed both BCG's and cleaned them both VERY WELL! I still need to replace the extractor on the Ramped bolt, but it performed very well today.

3) Magwell - Took the new bottom loading magwell, with a hammer, I worked the ejector so it would ride very close to the bolt, but did NOT touch the bolt. I then adjusted the placement of the ejector so it was sure to hit the center of the brass.

4) Mags - I had a variety of new and old C-Products 32 rd (Version 1 & 2) Magazines. I did not have to do anything for these to function properly.

5) GRIP on the gun! I believer this was the most important and impacting change I made. I typically shoulder the weapon with the support hand on the Magwell and Magazine. For 5.56 magazines this is not an issue. I found that by moving my had to the forearm of the weapon and ensuring that I am not pushing, pulling or impacting the placement of the magazine, the gun worked properly. This was an instance change in performance.

After a little working, it went well. Taking what I had learned, I was able to successfully drop all the ammo I could find down range. Now that the ejector is in place, I feel good with the weapon. I look forward to my next trip.

Thank you, Rob, for your help and suggestions!

 

[Rob72]

5) GRIP on the gun! I believer this was the most important and impacting change I made. I typically shoulder the weapon with the support hand on the Magwell and Magazine. For 5.56 magazines this is not an issue. I found that by moving my had to the forearm of the weapon and ensuring that I am not pushing, pulling or impacting the placement of the magazine, the gun worked properly. This was an instance change in performance.

You're welcome, but I have to say, I feel stoopid! I'm so used to grabbing the forend on my long guns, the mag hold didn't even occur to me.

Glad its running "great guns" now!