9mm AR problems...

[mike_c70]

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.

[L4D]

wait.. the buffer stays back in the tube compressed on the last round?

[bonesurf]

Buy my ASC mags. Explain the last round problem again? The promag mags suck. The magwell by them is ok. Which buffer? A RRA type or spikes type?

[mike_c70]

Sorry for the crappy description. After disenganging the bolt catch, the bolt won't fully return.

Finished taking the rifle apart. Looks like there was a pretty significant burr on the inside of the buffer tube. I guess it was either catching the spring or getting hung up on the bolt cuz there's a nice scratch on the bolt. After clearing out the culprit, seems to function check fine.

Just gotta figure out what's causing the dents in the bullets. Feedramp issues?

@bonesurf - using the 9mm Q buffer and spring from heavybuffers.com

Update: added pics for clarification.

Can smooth out the feed ramp to get rid of the sharp corner?
Another thing I found, looks like the buffer catch pin is all bent out of shape? Too strong buffer and spring?
Can anyone tell me if the ejector is in the correct place with the bolt face?






Thanks again!

[bonesurf]

Your bolt retaining pin looks wrong/bent to me. I will check my bolt tonight. Your feedramp is that scratched up????? Why?????

The promag a have a bad rep. Colts. ASC.

[Intimid8tor]

As far as the buffer retaining pin, it's crap now. Looks like the bolt is going too far back and then when it comes forward the buffer is slamming into the retaining pin. Either 7 quarters, a delrin spacer or a longer 9mm bolt to solve for that. Will probably also solve for future broken bolt hold open levers.

As far as feeding issues, make sure your ejector is riding really close to the slot in the bolt. You want it running as close to the top and to the center side of the grove in the bottom of the bolt. Quite often these have to be adjusted when working on getting a 9mm to run. In answer to your question, it needs to be higher in the groove. Can't tell if it is riding close enough to the wall of the channel.

As far as dented bullet tips. Feed ramp would be a start and make sure mags are sitting high enough in the block. As for mags, I would recommend metalform. I have some c products which are now MSC and they can be hit or miss.

[glock 357]

Did you buy that AR complete or did you put it together yourself? I only ask if purchased complete, take it back should have warranty I'd imagine. Or if put together yourself, if you feel comfortable doing it and know how, round off those edges if that will help. Not saying it will, I've never experienced feeding issues. Good luck.

[mike_c70]

@bonesurf - Wasn't sure what a 9mm feedramp should look like. That's what I'm trying to figure out as well.

@Intimid8tor - figure the pin was scrap metal. As mentioned I got the spring and buffer from heavybuffers.com per recommendations from the board. Should I swap out and got with a regular carbine spring and buffer? Or is this purely a spacing issue? You mean add a delrin spacer to the other end of the spring?
How do I get the mags to sit higher when it's a dedicated lower?

@ glock 357 - Upper was bought completed from jsesurplus (incl cmmg ramped bolt). I just swapped out the handguard. Lower is a dedicated CMMG lower. I put the LPK in myself.

Where do I find 10rd metalforms? Don't think they even make them.

[Intimid8tor]

@bonesurf - Wasn't sure what a 9mm feedramp should look like. That's what I'm trying to figure out as well.

@Intimid8tor - figure the pin was scrap metal. As mentioned I got the spring and buffer from heavybuffers.com per recommendations from the board. Should I swap out and got with a regular carbine spring and buffer? Or is this purely a spacing issue? You mean add a delrin spacer to the other end of the spring?
How do I get the mags to sit higher when it's a dedicated lower?

@ glock 357 - Upper was bought completed from jsesurplus (incl cmmg ramped bolt). I just swapped out the handguard. Lower is a dedicated CMMG lower. I put the LPK in myself.

Where do I find 10rd metalforms? Don't think they even make them.

RRA makes a dedicated spacer that fits in the end of the buffer tube to stop overtravel. The same can be accomplished with 7 quarters if using a standard 9mm buffer. Looks like spikes sells a spacer that can be put in as well.

http://www.spikestactical.com/new/z/lower-parts-spikes-st9bs-stt2-combo-9mm-p-235.html

The goal is to stop the bolt from traveling too far back and then coming forward with a head of steam bending and breaking stuff. I run a spikes ST-9x which is a long buffer. I don't think you want to go just to a standard carbine buffer. All of this is assuming you are running a carbine tube and not a rifle tube.

As for magazines, forgot about the 10 round deal. You could try colt and see if they make 10 round or go with MSC. I did find their 10 rounders were more consistent than the larger capacity.

Tough to get the mag to sit up higher since it is dedicated. I would probably speak with cmmg. Are the feed ramps pressed all the way down? It seems the ramp is the issue with the bullet denting.

[missiondude]

As far as the buffer retaining pin, it's crap now. Looks like the bolt is going too far back and then when it comes forward the buffer is slamming into the retaining pin. Either 7 quarters, a delrin spacer or a longer 9mm bolt to solve for that. Will probably also solve for future broken bolt hold open levers.

As far as feeding issues, make sure your ejector is riding really close to the slot in the bolt. You want it running as close to the top and to the center side of the grove in the bottom of the bolt. Quite often these have to be adjusted when working on getting a 9mm to run. In answer to your question, it needs to be higher in the groove. Can't tell if it is riding close enough to the wall of the channel.

As far as dented bullet tips. Feed ramp would be a start and make sure mags are sitting high enough in the block. As for mags, I would recommend metalform. I have some c products which are now MSC and they can be hit or miss.

I did the 7 quarter trick, but thought that was to keep the overtravel of the bolt down so that the bolt release does not get the crap beat out of it. The bolt is supposed to keep the buffer from smashing into the buffer stop pin. Mine pushes the buffer back just slightly when I close the rifle. My pin just keep the buffer from flying out when the rifle is taken apart. Sounds to me like he got an out of spec bolt, and it may explain the feeding issues as well. Op, do you have calipers that you could measre the OAL of the bolt? Post up the length and some pics of the bolt. I have never seen a buffer retainer beat to crap like that before.

[Intimid8tor]

I did the 7 quarter trick, but thought that was to keep the overtravel of the bolt down so that the bolt release does not get the crap beat out of it. The bolt is supposed to keep the buffer from smashing into the buffer stop pin. Mine pushes the buffer back just slightly when I close the rifle. My pin just keep the buffer from flying out when the rifle is taken apart. Sounds to me like he got an out of spec bolt, and it may explain the feeding issues as well. Op, do you have calipers that you could measre the OAL of the bolt? Post up the length and some pics of the bolt. I have never seen a buffer retainer beat to crap like that before.

That's a really good point that I had totally forgotten about. I spoke wrong since the bolt should stop it from coming too far forward and hitting the pin.

[mike_c70]

Here's a picture of the Q buffer:

It looks like the length is accounted for. Looks to be a weight issue now or the spring is too strong.

Feed ramp looks like it's pressed in properly:
Unless the ramp was machined incorrectly height wise.

OAL of CMMg bolt is 169.60mm

[Intimid8tor]

Here's a picture of the Q buffer:

It looks like the length is accounted for. Looks to be a weight issue now or the spring is too strong.

Feed ramp looks like it's pressed in properly:
Unless the ramp was machined incorrectly height wise.

OAL of CMMg bolt is 169.60mm

Good job posting pics for us to look at. Makes it so much easier to try to diagnose issues. I misread in your first post. Thought you were using the ST-T2 buffer already.

The post just before my last one I think hit on something. The buffer should never hit the pin coming back forward as the bolt should hold it back. That issue could be caused by an out of spec bolt. I'm also wondering about the location of the buffer retainer detent pin. It seems to be too far forward. If that is the case, I wonder if the buffer tube is threaded too far in and this is causing the buffer to slam into the back of the tube and bounce forward. Somehow, the fact that the pin is severely bent is related to this. May not be the cause, but I think that it is somehow related.

[mike_c70]

I'm also wondering about the location of the buffer retainer detent pin. It seems to be too far forward.

I compared the 9 lower to 3 other lowers I have, looks the same to me. FCG cutout seems to be in the right place as well.

I think I'm going to be RifleGear a visit tomorrow to ask them for help since I got the lower from them. They have 10/20 metalforms in stock as well which I'll try out. The buffer pin bending still baffles me though.

[Intimid8tor]

Sounds like a good call. Let us know what you find out.