My 9mm AR was filthy

outrider58 · Sep 3, 2017

boss281 said:
Hope they work for you. But 5.56 needs love too every now and then! But 500 rds and barely any grime, sheesh!

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You aughta see the inside of mine!

inkd · Sep 3, 2017

j_h_smith said:
Those WWB 115gr round are some very filthy rounds. Probably the dirtiest I've ever fired. It wouldn't surprise me if those are the source of some of your problems.

Try a little better round and see if that makes a difference.

Ran some 124gr reloads through it tonight and it was a huge difference.

boss281 · Sep 4, 2017

If you try the Winchester 90g SuperClean and 147g WinClean the grit on the brass is barely noticeable.

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outrider58 · Sep 10, 2017

Went to the range on Friday and this happened... :cool:

outrider58 · Sep 10, 2017

Did some reading up on PPU brass and people either have had problems with PPU brass or they haven't. Most of the problems are rooted in neck tension/bullet push back leading to higher pressures. I've got maybe 1500 rounds through this gun and this is the first time I have seen this. I'm going to go through the rest of my reloads and pull/test all the PPU cartridges. All the ammo shot through this gun have been reloads. No factory ammo at all.

j_h_smith · Sep 10, 2017

outrider58 said:
Went to the range on Friday and this happened...

What you go and do that for? :innocent0

That sucks. Are those the only rounds that did this or are we talking about many more?

outrider58 · Sep 10, 2017

j_h_smith said:
What you go and do that for?

That sucks. Are those the only rounds that did this or are we talking about many more?

I cleaned the batch from the range trip(about 200 rounds) and will inspect them probably later today if I get the chance. Meanwhile, I've order a heavier buffer just because.

threegun · Sep 10, 2017

I am running a heavy buffer and a Tubbs flat spring and am having the same problem with the PPU rounds when using the Magpul Glock magazines. The problem seems to be limited to the last one or two rounds in the mag. One round blew out the side of the case. I was running suppressed without ears, I couldn't hear out of my right ear for a week. The problem seems to be bullet push back. I have not experienced the problem with Glock factory magazines, but I am using three Magpul mags to one Glock mag so I can't say for sure it is mag related or just the percentages working against the Magpul. Next trip I will only use Glock mags and see what happens.

j_h_smith · Sep 10, 2017

This isn't looking good for PPU ammo. I hope you're okay. Having that happen without hearing protection had to hurt. I've never bought PPU ammo, but rest assured, I won't look at it from this point on.

Take Care.

outrider58 · Sep 10, 2017

threegun said:
I am running a heavy buffer and a Tubbs flat spring and am having the same problem with the PPU rounds when using the Magpul Glock magazines. The problem seems to be limited to the last one or two rounds in the mag. One round blew out the side of the case. I was running suppressed without ears, I couldn't hear out of my right ear for a week. The problem seems to be bullet push back. I have not experienced the problem with Glock factory magazines, but I am using three Magpul mags to one Glock mag so I can't say for sure it is mag related or just the percentages working against the Magpul. Next trip I will only use Glock mags and see what happens.

I'm using Colt style mags, suppressed as well. I was using 147 gr Blue Bullets.

threegun · Sep 10, 2017

I was using the 147 gr JHP. A few rounds would partially chamber after the push back, but the hammer wouldn't drop on the open bolt. I could see a scar on the nose of the bullet and a small bulge in the case from the bottom of the bullet. After the blow out I looked at some of the fired case and found bulges like yours. I guess there is a point where the hammer will fall on a slightly open bolt.

outrider58 · Sep 10, 2017

All the bulges on mine seem to be at the web, kind of like a "Glock bulge"

rayrevolver · Sep 10, 2017

Are those out of battery???

I have had 10mm cases look like the one on the right in a 1991 G20. The other two are scary! Glad there wasn't a big boom.

EDIT: Sorry, saw you said bullet pushback. Dang!

bfoosh006 · Sep 11, 2017

outrider58 said:
Went to the range on Friday and this happened...

I don't remember... what buffer weight and buffer spring ?

( Glad you didn't have a blow out. )

outrider58 · Sep 11, 2017

bfoosh006 said:
I don't remember... what buffer weight and buffer spring ?

( Glad you didn't have a blow out. )

KAK standard configurable buffer (with 3 tungsten weights) and Tubb's 308 flat wire spring.

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outrider58 · Sep 11, 2017

rayrevolver said:
Are those out of battery???

I have had 10mm cases look like the one on the right in a 1991 G20. The other two are scary! Glad there wasn't a big boom.

EDIT: Sorry, saw you said bullet pushback. Dang!

I'm not sure about the pushback.
Only guessing. The bulges seem to confined to the web. Doesn't appear (to my ignorant eyes) to be OOB.

I have read a lot about the .40 Glocks having a similar problem due to an unsupported barrel, but I believe they fixed that in later generations.

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photoracer · Sep 11, 2017

They look like out-of-battery ignitions, which is possible on just about any blow-back action from .22LR on up. And since we are all building them ourselves in many cases I'm surprised it does not happen more often. Many reasons can make it happen.

Bountied · Sep 11, 2017

out of battery

I had a case on my 9mm AR blow out. It turned out to be an unfinished chamber not letting the bolt close all the way. The brass would snag on the rough edge. I guess it was just in battery enough to allow the hammer to hit the firing pin. I got a face full of gas. Some shrapnel bounced of the wall and hit me also. I checked the barrel and the bullet was stuck in there.

If your chamber is/was super dirty it could prevent the round from fully chambering.

To fix mine I took a jewelers round file to remove the sharp edge and then polished it with a dremel. No issues since, but I always clean my firearms as soon as I get home before I take them back out to the range. The last time I shot the 9mm AR I put 450 round through it with zero issues. I use the stock buffer and spring in mine. I also use glock mags only.

Bountied · Sep 11, 2017

This is it

jimbobborg · Sep 11, 2017

After my dumpster fire showing this past weekend, I ordered a new CMMG 9mm BCG. It should be here Thursday. I have no idea what the current BCG is in mine, and I doubt it's a CMMG. I'm going to get a mag well funnel and install it after this weekend. I'm hoping I can get through all of the stages this weekend without any FTEs. I'm testing it Friday night, along with my new Armscor 9mm 1911.

My 9mm AR was filthy

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