300 Blackout AR Malfunctions

[darkfader]

I’m hoping you guys can help me out with this damn thing. I’ve never been able to get it function properly and I’d really like to have it working.

300BO
AERO upper and lower and aero mil-spec internals
8.5” Ballistic Advantage barrel w/ pistol length gas
Standard carbine buffer and spring
Aero adjustable gas block

Barrel has been dimpled for the gas block and the carbon fouling verifies good placement. Block and tube flow air freely when off the rifle as well.

I’m interested in running some Hornady Black 208gr AMAX rounds with a Dead Air Sandman S.

Or any damn round really.

At every click of the AGB, there is no lock back on an empty mag and no chambering of the next round in the mag. Doesn’t matter if Pmag or Okay Industries steel mag or Duramag. Doesn’t matter, won’t work.

I’d be grateful for any insights on what I can do to improve this thing other than disassembling and adding to the parts bin. I have a ton of different 300 ammo, can’t get subs or supers to work right.

Aero customer service suggested it was overgassed a year ago or so, but I can choke the AGB down to where there’s no ejection at all so I just don’t think that’s the problem. If there’s a comprehensive thread somewhere about 300 builds I’d love a link. Thanks for any help. I’m about to give up on it.

 

[USK308]

What is the weight of your buffer? Standard weight buffer isn't going to work with your setup (to my knowledge).

Are you starting out with the AGB wide open, shoot 1 round to check for lock-back? FWIW, I tried an Aero Precision AGB first but it would NOT work for $h!t...so I put a spare SupArms AGB on and after a little work to dial in....boom, I was good to go.

When I was working to dial-in my 300BLK SBR (10.5" barrel), the Hornady 190 Sub-X and the 208 A-Max were just GARBAGE. The 190 Sub-X was only marginally better than the 208 A-Max, where the 208gr A-Max never would lock back.

I finally found that 200gr S&B, 200gr Winchester Open Tip or 220gr Fiocchi Range Dynamics were the rounds that worked for me with my Otter Creek Labs Hydrogen L 7.62 suppressor. I'm running a JP H2 buffer (JPSCS15-H2) and a Superlative Arms AGB. My AGB is set at 19 clicks and the rifle runs like a dream (now) with the aforementioned ammo!

 

[darkfader]

Thanks a lot for that. I figured Hornady was G2G. I have some Fiocchi I think, I’ll check. I’ll see about a superlative arms AGB and play with buffer weights and see what happens. Thank you very much USK308!

 

[USK308]

Thanks a lot for that. I figured Hornady was G2G. I have some Fiocchi I think, I’ll check. I’ll see about a superlative arms AGB and play with buffer weights and see what happens. Thank you very much USK308!

While I have found Hornady ammo to be pretty good in other calibers in the past, there have been a fair number of people AND reports of Hornady ammo issues. Hopefully you can find some ammo that does work for ya and get that gun running smooth as butter!

 

[hlee]

Hornady black doesn’t lock back on empty in my 300 BO, but it runs otherwise. Can you lock the bolt back on an empty mag just by pulling the charging handle? A buffer that is too long, or an extension that is too short could give a false short stroke symptom. And, over gassing can cause the bolt to outrun the magazine.

I’m pretty sure S&B loads locked back in my gun.

But, I worked up a sub load using A1680 and 208 AMAX bullets that runs and called it a day. Well, not exactly. I also made a load with 150 gr round nose as well as 125 gr bthp (both super sonic). Then, I called it a day.

 

[Sterlingb06]

I’m hoping you guys can help me out with this damn thing. I’ve never been able to get it function properly and I’d really like to have it working.

300BO
AERO upper and lower and aero mil-spec internals
8.5” Ballistic Advantage barrel w/ pistol length gas
Standard carbine buffer and spring
Aero adjustable gas block

Barrel has been dimpled for the gas block and the carbon fouling verifies good placement. Block and tube flow air freely when off the rifle as well.

I’m interested in running some Hornady Black 208gr AMAX rounds with a Dead Air Sandman S.

Or any damn round really.

At every click of the AGB, there is no lock back on an empty mag and no chambering of the next round in the mag. Doesn’t matter if Pmag or Okay Industries steel mag or Duramag. Doesn’t matter, won’t work.

I’d be grateful for any insights on what I can do to improve this thing other than disassembling and adding to the parts bin. I have a ton of different 300 ammo, can’t get subs or supers to work right.

Aero customer service suggested it was overgassed a year ago or so, but I can choke the AGB down to where there’s no ejection at all so I just don’t think that’s the problem. If there’s a comprehensive thread somewhere about 300 builds I’d love a link. Thanks for any help. I’m about to give up on it.

Gas block alignment is still problematic here even with the check on dimpling and fouling. Twist it, untwist it, twist it again to ensure maximum setting. A standard carbine buffer could possibly be a tad on the heavy side for your configuration going with a subs trying a lighter carbine buffer might prove beneficial. Adjusting the elevation with different supersonic or subsonic values could also tell if your rifle is choosy about ammo. Finally, ensure that you’ve measured the gas port size twice. Sometimes such barrels are shorter with pistol-length gas systems require adjustment to generate enough gas.