16" carbine length

[Timmay]

Sorry if this has been hit on before, but I'm new in the forum.

I have a diamond back ar-15 with 16" barrel & carbine gas system. It's only had a couple of hundred rounds through it, and up til now has been 100% reliable. I had been only using 150gr Ammo Inc FMJ super sonic rounds with 5.56 magazines.

This weekend I tried some AAC 125gr FMJ supersonics and it couldn't cycle more than 3 rounds before it would chew up a cartridge trying to feed it. It also failed to lock the bolt back on the last round half the time. I went back and tried the same mag with the 150gr ammo, and the gun worked great.

I also had my 7.5" 300 BLK AR pistol there. It ran the same mag with the 125gr ammo just fine.

I haven't had time to dig into the gun and check the BCG and gas system, but I would like to leverage the knowledge base here before I get too far.

TIA

[Timmay]

Sorry, I forgot to mention: I'm never gonna run suppressed, and I'm never gonna run sub sonics. I'm only running 110-150gr supersonics

[gds]

Drill gas port to .125. Most carbine length 300blk have too small a gas port in my opinion.

[Timmay]

I went ahead and checked BCG, and everything looked ok. I couldn't measure gas hole, but I eyeballed it around ~0.95 to 0.100. I went ahead and drilled it out to 0.125

I'll try to get out next weekend to try out and I'll report back results. Thanks.

[dellet]

It would be helpful to others if you would let us know the ammo used. As far as I know, AAC (Advanced Armament Corp) never made ammo.

The reason being any ammo that will not cycle 16” carbine gas rifle that is properly set up, with a gas port larger than .090”, quite simply is crap. It might save others some grief knowing not to buy it.

[Timmay]

https://palmettostatearmory.com/aac-300 ... d-box.html

My 7.5" pistol ate through it no problem.

[dellet]

I was interested in who American ammunition company was, as their logo is very similar to Advanced Armament Company, who brought 300 Blackout to market.

First review I found of the ammo was basically the same problem you described, no jams, but not locking back. No mention is gas system and added that brass all ejected extremely forward. In itself maybe not an issue, but the review included velocity and spread numbers. The extreme spread 150 fps, and standard deviation 50 fps, were terrible.

Without knowing more about your rifle, hard to say the actual problem. I would not be surprised if it was actually over gassed, instead of under. You’ll know when you shoot next.

Based on the one review I looked at, and your description, I fall into the ammo is crap camp. The numbers explain the 2” groups at 100 yards. Honestly this is why the cartridge got an early reputation as unreliable and not capable of any decent accuracy.

2012-15 were years of ammo and component shortages, anybody with a press and powder became a “manufacturer” and cranked out crap ammo. I think that may be the case here.

https://m.youtube.com/watch?v=GibJJLAXE94

And yes, it is very easy to over gas a carbine length gas system. No matter what the “experts” say.

[Timmay]

Nice points. Well I'll find out this weekend whether I went the right direction. If not, I guess the next step is dialing it back with an adjustable gas block.

[dellet]

I wouldn’t worry about it until you’ve tried more, different ammo. Plenty of carbine barrels out there with .125” ports. If you have one in the pistol, an H2 buffer can help if it’s over gassed.

Which brings the question of what buffer is currently in the lower, should be an H. About 3 Oz. Pistol gas an H2.

Something to keep in mind is that for the action to be able to cycle with subs, it will automatically be over gassed for supers. Trying to split the difference means everything needs to be within a small window. Ammo specs become critical. When you see ammo throwing triple digit velocity spreads in four different rifles, it’s impossible to blame anything else but the ammo. Maybe the chronograph, but it's not the rifles.

Look forward to results

[Timmay]

I don't plan on ever shooting subs. I live in Illinois, where silencers aren't allowed. I only plan on using 125-150gr FMJ and 110-150gr hunting rounds. I will be using this gun this fall as a single shot (0-round magazine/sled) deer rifle. I know 300 BLK may not be the best for deer, but I chose this gun because its a good compromise between hunting, home defense, & fun range shooting.

As far as buffer, it's not marked so I'll have to pull it out and weigh it. I assumed it was a H1. I'll check it this weekend. Thanks