AAC 9" 300BLK malfunctions unsuppressed

[Eurodriver]

I didn't know whether to put this in the reloading section or here, but figured the chances of someone with knowledge of the platform seeing it would be higher here.

I have an AAC 9" 300BLK with an A5 buffer. Functions 100% with Fiocchi supersonic unsuppressed and suppressed, and 100% with Gemtech 187gr subsonic unsuppressed and suppressed. (Doesn't lock bolt back unsuppressed with subs, but no malfs)

I shot my first reloads today, about 200 of them. It ran 100% suppressed.

Unsuppressed, I got failure to ejects. (empty case on top. New case trying to feed on bottom)

http://i1328.photobucket.com/albums/w521/6234987u02/IMG_2607%201_zps5sm7r9ya.jpg

Cases

http://i1328.photobucket.com/albums/w521/6234987u02/IMG_2608_zpsqk4bvcoa.jpg

Any ideas?

I was running

M80 bullets
LC Brass cut to 1.358"
OAL was 2.065"
15.8gr Win 296
CCI 400 Primer

Again, functioned 100% suppressed whether firing rapidly or slowly, full mag or empty. But it would not get through more than 5 rounds or so unsuppressed without failing similar to the picture above.

Ideas? I was concerned my powder charge may be too low, the max is 16.2gr IIRC, but I've been reading about guys running 18 grains?

[tom12.7]

1. Make sure the ejector functions smoothly and properly.
2. I don't run that load, but it could be underloaded, bump it up .2gr at a time and look for pressure signs.

[Onyx Z]

Nah, that load should work well and it should function 100%. If it is stripping another round from the mag, the BCG is cycling far enough. I would say it is a weak ejector or extractor. A5H2 buffer?

18gr H110/W296 is pretty hot for a 125gr bullet, much less a 150gr bullet.

[Charlie Don't Surf]

I was getting FTEs unsuppressed about 400rds into the life of the gun on my 300blk, I installed the O-ring on the extractor spring and the problem went away.

ETA: It was a Bravo Company BCG. Happened with several loads, on both a H2 and H3 buffers

[BC98]

Euro,

I would first try bumping the load. Hodgdon's website lists a max charge of 16.2gr with a 150gr Hornady Interbond bullet. The lengths between the IB and M80 should be close. You might be able to push it further but do so with caution and keep an eye out for pressure signs. Another possibility is that 296 might not have quite the right burn rate to generate the necessary gas volume to cycle your action. With 145gr and above, I've only used A1680 or Lil' Gun but they've cycled my gun (same upper and buffer as you are running).

[BC98]

Nah, that load should work well and it should function 100%. A5H2 buffer?

18gr H110/W296 is pretty hot for a 125gr bullet, much less a 150grgr bullet.

He's only running 15.8gr of H110. I have to look at my load data but I believe I've worked up to 19.2gr of H110 with a 125gr Speer TNT with no issues.

[Onyx Z]

He's only running 15.8gr of H110. I have to look at my load data but I believe I've worked up to 19.2gr of H110 with a 125gr Speer TNT with no issues.

Yes, but he mentioned people running 18gr. In my experience, 18.2gr H110 under 125gr SMK's was very hot load. But it would stack SMK's (<.5moa), so it was well worth beating up the brass.

[domestique]

I've never used VLTOR's buffer system, but the 9" was designed to run the H2, and the 16" a H IIRC. I'm sure the man that helped design and test them will be along shortly.


What BCG are you using? It doesn't look like AAC's factory carrier.

[Eurodriver]

I've never used VLTOR's buffer system, but the 9" was designed to run the H2, and the 16" a H IIRC. I'm sure the man that helped design and test them will be along shortly.


What BCG are you using? It doesn't look like AAC's factory carrier.

I know, but it does work with the A5 and factory ammo.

It's a USGI BCG.

[BC98]

I've never used VLTOR's buffer system, but the 9" was designed to run the H2, and the 16" a H IIRC. I'm sure the man that helped design and test them will be along shortly.


What BCG are you using? It doesn't look like AAC's factory carrier.

The OP stated that his A5-equipped gun runs factory loaded ammo (subsonic and supersonic) in both suppressed and unsuppressed conditions. The issue comes in when he runs his first reloads. If it runs fine with factory ammo and the A5, then it seems like it should run fine on a good handload.

FWIW, I have the same upper and run my lower with the A5 system and run an VLTOR H4 buffer (7 oz). Unsuppressed, my gun will cycle and lock back factory Remington supers and subs, Federal subs, and all of my supersonic handloads.


Onyx Z,
You are correct about the charge weight mentioned initially. I neglected to read the last section of the post closely enough.

ETA: Dammit, Euro beat me to it...

[domestique]

I know, but it does work with the A5 and factory ammo.

It's a USGI BCG.

I would try another BCG before I blame the reloads.

I'm assuming your brass looked good afterwards? (No flattened primers, streaking etc.?)

Was the ejection pattern the same as factory loads?

[tom12.7]

Initially, I didn't notice the non current AAC BCG. When the early AAC 300 9" guns came out, there was some issues with some subs with the A5 without a can for me. My newer AAC 9" guns run great with the A5 system. Robert had posted that he didn't think that the porting has changed, and they obviously wouldn't make a carrier that was less reliable and market it.
When I finally had a sample size of their newer carriers, I mapped out the changes and I'm still testing them out.
From what I've seen so far, I would find an AAC BCG, then test loads from there.
As to the posting of using heavier than than the A5H2, towards the A5H4 with subs and no can, there can be other issues at hand.

[Eurodriver]

I sold the AAC BCG. Gun runs fine with the USGI.

It is ammo related. Not BCG related.

I'll tweak adding more powder, using different powders, and adjusting OAL. I'm not dropping $200 on an AAC BCG to replace a carrier. That buys a lot of components, and there isn't anything special about an AAC over a USGI that would cause malfunctions except perhaps an extractor o ring.

Ironically, a buddy of mine also has an AAC 9" and his rifle would malfunction with the AAC BCG until he switched to a BCM carrier.

https://www.m4carbine.net/showthread.php?150153-9-quot-AAC-300BLK-failing-to-extract-while-unsuppressed

[domestique]

I sold the AAC BCG. Gun runs fine with the USGI.

It is ammo related. Not BCG related.

I'll tweak adding more powder, using different powders, and adjusting OAL. I'm not dropping $200 on an AAC BCG to replace a carrier. That buys a lot of components, and there isn't anything special about an AAC over a USGI that would cause malfunctions except perhaps an extractor o ring.

Ironically, a buddy of mine also has an AAC 9" and his rifle would malfunction with the AAC BCG until he switched to a BCM carrier.

https://www.m4carbine.net/showthread.php?150153-9-quot-AAC-300BLK-failing-to-extract-while-unsuppressed

I think another difference is the extractor spring they use IIRC. I believe they mention it in their manual. There is a pdf on Google.


As long as your BCG works in other guns then I think your right in assuming it's the reloads.... but they seemed in line with everyone elses.

You could always run your bcg in your buddies 9".

[tom12.7]

I would agree that it's most likely an induced issue from the ammo, but there is at least some data that suggests a broader range of function is possible in this with the factory parts in the upper with the A5.

[Eurodriver]

I think the only difference is the extractor spring they use IIRC. I believe they mention it in their manual. There is a pdf on Google.


As long as your BCG works in other guns then I think your right in assuming it's the reloads.... but they seemed in line with everyone elses.

You could always run your bcg in your buddies 9".

Good point about running it in my buddies. I'll look into the extractor sprint I didn't know about that.

I also have a lower with an H2 buffer that I can try, but I'd rather figure out what makes this ammo different than factory (which works fine) rather than go adjusting and changing parts on the gun. It just seems backwards to me. I'd rather chase the reloads and make them function with the gun, instead of making my gun function with the reloads.

[domestique]

Good point about running it in my buddies. I'll look into the extractor sprint I didn't know about that.

I also have a lower with an H2 buffer that I can try, but I'd rather figure out what makes this ammo different than factory (which works fine) rather than go adjusting and changing parts on the gun. It just seems backwards to me. I'd rather chase the reloads and make them function with the gun, instead of making my gun function with the reloads.

Totally get trying to get reloads to work (especially since factory rounds work). I would just hate to see someone blow a punch of components when a BCG and 30 cent spring may be the issue.

Good luck!

[StikkershokK]

Gas block is clean?


Happy trails.

[Onyx Z]

I seriously doubt it is an ammo issue. .4 gr under max is not a lot, nor should it be enough to cause a malfunction. If it functions when bumping it up to max, it would likely mean you are running on the edge or reliability. But then the mfgs recommendations are usually very conservative, so take that FWIW...

Does it lock back on empty unsuppressed with your super loads? I'm thinking you need a heavier buffer since it is cycling enough to strip another round. If you have somee unused carbine length buffers laying around, the weight inside of the A5 buffers are the exact same, so you can swap them around to build your own A5H3, H4, etc. You don't need to drop $60 on an A5 specific buffer.

[Eurodriver]

Today I shot a bunch of loads. Function was 100% with 16.0gr-16.8gr (in 0.2gr increments) of W296 at 2.125" and 2.140" OAL . All variations worked.

I'm not sure what the issue was, whether it was related to OAL or charge, but it all cycled beautifully.

With that said, I have seen some really insane loads published online! I was getting pressure signs at 16.8gr. They were so bad, that the guy next to me picked up some of my brass to help me out and even said "Whoa buddy! These look a little hot!" and he didn't even know I was testing max loads.

I made more loads all the way up to 17.8gr but I didn't shoot them when 16.8gr already looked dangerous. How in the world are people running such high charge loads? http://www.300blktalk.com/forum/viewtopic.php?f=141&t=78308&hilit=M80+starting&start=50 There is a guy running 18.1 grains!

Anyway, again, not sure if the charge or OAL is what cured the issue but it seems to be fixed now. I am happy that I can begin loading tons of 300BLK now.

[rsilvers]

I would check the extractor and ejector.

If you have more than several thousand rounds on it, then replace the extractor spring. Depending on what kind of extractor spring you have, you may want an o-ring.

[GunnutAF]

Pistol gassed - run pistol buffer! Buffer not light enough for your load. Lighter spring maybe. Your A5 buffer obviously needs the extra pressure generated by the Suppressor. I run a 16" Carbine gas 300 Blk and have had zero issues with any load I've run. And it's not suppressed.

[Iraqgunz]

If you guys care to read, he has apparently resolved the issue.

[Vash1023]

its almost certainly your extractor ... who manufactured your BCG? i had a CMMG bolt do the same thing. switched out the shitty factory extractor parts and it runs fine now.

my bad. didnt read the whole thread....