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Page AR-15 » Rimfire and Pistol Calibers
AR Sponsor: bravocompany
Posted: 10/14/2017 9:15:46 PM EDT
I just received my Griffin Armament Optimus and took it out for the first time today. Ran several mags of 5.56 through an SBR and then decided to switch over to 9mm AR pistol. Three lug mount/configured properly. Ran a couple mags of Blazer Brass 124gr suppressed with no issues except a couple where it didn't cycle. Loaded some PPU 158gr subsonics, which I'd never tried before. After one or two, what seemed like a kaboom occurred. Different sound, gas everywhere and mag blown out the bottom but no damage to gun.

Loaded a few more and tried again. Same thing after a couple rounds. Took the suppressor off and went back to Blazer 124 gr. Same thing happened again after 2-3 rounds.  Decide I'm done with that gun, and go to put it away. Rack the charging handle a few times and the small piece of brass in the pic below falls out. Found the casings from the kabooms- also pictured below. Trying to figure out what the issue is and hope you guys can help. Questions:

1. This is my first suppressor so first question is what would be the fix for it not cycling with 124gr ammo?  Buffer?  Spring?  Lube?

2.  Seeing  the bulged cases makes me think firing out of battery. Thoughts?  

3.  Is it possible that the ripped up casing left a piece of brass in the chamber or stuck between bolt carrier and upper and was preventing either the round from fully chambering or bolt heading all the way home this causing OOB firing?

4.  This is a pistol with a blade brace and I was cheek welding it, not shouldering it. Is that like limp wristing a pistol an causing issues?  

5.  What would your next steps be?  I want to get some opinions before I fire it again.  

ETA - pieces of the follower got broken off during all of this. See the mag in the pic.

Attachment Attached File
Link Posted: 10/14/2017 10:26:30 PM EDT
[#1]
What kind of FCG is in the gun?
When it did the thing, did it seem like it fired more than once?  Like you pull the trigger, gun shoots, then it shoots again but the second shot was OOB and blows the magazine out the bottom of the gun?
Link Posted: 10/14/2017 10:30:00 PM EDT
[#2]
Possibly but I don't think so. If so, what would cause that?  Bolt bounce?

FCG is whatever the PSA 9mm lower comes with. Is there something that should be changed?  

Fired fine before without suppressor and with 115 and 124 gr ammo.
Link Posted: 10/15/2017 8:25:53 AM EDT
[#3]
Tell us about the recoil system.  What buffer/spring combo are you using?
Link Posted: 10/15/2017 4:43:36 PM EDT
[#4]
I'm no gunsmith, but I'm guessing the FCG.  Disconnector not catching the hammer good enough.  Hammer drops when its not supposed to and whacks the firing pin before the next round gets all the way in the chamber.

Reason I'm guessing that is because I had a PSA glock 9mm lower that did something similar.  I never ran it suppressed.  But the first time I had it out, in the first few hundred rounds, it OOB'd and blew the magazines out of the magwell 3 times.  It also double and triple fired a couple times.  I sent it in and they said the FGC was not quite right and replaced it.  Yours may be something silly like shooting with the suppressor caused some extra filth to get into the FCG and make it not function properly.  That would explain why it still doesn't act right even with the can removed.  I'd try cleaning it up and/or swapping the FCG out.  While you're at it, scrub the chamber and make sure rounds can drop all the way in freely.
Link Posted: 10/15/2017 8:54:01 PM EDT
[#5]
Link Posted: 10/15/2017 9:06:06 PM EDT
[#6]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
My guess is that you're using a solid buffer and an extra powered spring.

You are getting bolt bounce and the round is coming back quickly from the bounce while the firing pin is still going forward and it is igniting the primer.

You NEED a buffer with sliding weight and a regular carbine spring.

This is my favorite 9mm buffer:

https://www.kakindustry.com/ar-15-parts/lower-parts/buffer-tubes-and-parts/pistol-buffer-tubes/ar15-9mm-buffer-long-heavy

Weighs 10.9oz and has sliding weights.

Use a carbine spring as well.

Until you do this, be really careful at where you're pointing your rifle when you are cambering a round. I suspect that you are getting an increased bolt velocity which is giving you increased bolt bounce and making rounds go off.

Having a BCG with a spring retained firing pin is also very good insurance.

Guys: Never use a solid buffer for 9mm ARs!!
View Quote
I'll give this a shot. Need to try a new buffer anyway. I'm using the standard 9mm buffer and spring from PSA. Guessing it's a standard carbine spring.

I'll clean up the FCG, try this buffer and see how it goes. Should I get the Wolff extra power spring as well or try swapping the buffer first?

Also, Josh, do you guys sell the buffer you posted?  I bought my brace from you guys and you were awesome. If I can buy the buffer from you, I will.
Link Posted: 10/16/2017 3:33:17 PM EDT
[#7]
Link Posted: 10/18/2017 11:25:06 AM EDT
[#8]
Those are bolt bounce OOB brass. I had the same thing happen when I used a soild buffer. Try a colt 9 mm buffer with moving weights and it should keep your fast trigger finger and bounce in check.

Are you using the stock trigger?
Link Posted: 10/19/2017 9:24:15 PM EDT
[#9]
Yep stock trigger. Spring feels pretty heavy.

Installed the KAK sliding weight buffer recommended above. Should I also use a buffer spacer?  I have it in there now. Should I take it out before trying it or keep it in and see how it does?  Still have regular carbine buffer spring.
Link Posted: 10/19/2017 11:36:07 PM EDT
[#10]
stock trigger?  you have a full auto trigger finger hahaha. I say that because OOB normally happen on very fast firing

I would use it without a spacer first and see how it functions.
Link Posted: 10/20/2017 9:32:37 AM EDT
[#11]
The KAK buffer should be slightly longer than a standard one so you shouldn't need the spacer.
Link Posted: 10/22/2017 1:42:57 PM EDT
[#12]
Update: installed the heavy KAK buffer and removed the buffer spacer and went to the range today. Worked flawlessly. Only fired 50 or so rounds due to time but fired 115 gr and 158 gr subsonics both suppressed and unsuppressed. Seeing I couldn't get more than 2-3 rounds without issue last time, I'd say it's headed in the right direction. Still not 100% confident in it, but hopefully will be after a few more range trips.

Thank you for the help Josh and all who weighed in!

I also used a magpul Glock mag today instead of ETS which I used last time. Any chance the mag could have been contributing to the issue?  It ran fine with ETS mags prior to last range trip when I had the issue.

On another note, the follower in the ETS mag broke from the OOB firing last time. I emailed ETS and asked if they sell just followers. They don't but they sent me some for free and even covered the shipping. Great folks!
Link Posted: 10/23/2017 10:57:32 AM EDT
[#13]
Mag is not the issue. Stay with the heavy buffer as others have suggested.
Link Posted: 10/23/2017 11:30:14 AM EDT
[#14]
It was the reciprocating mass in the buffer you needed. As long as you have that your OOB days are over for your build. Got you have it working and have fun!
Page AR-15 » Rimfire and Pistol Calibers
AR Sponsor: bravocompany
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