7.5" 300 BLK Pistol Issues

[Wildcat19]

Good Evening

I don't live in CA, so their dumb ***** laws don't apply to me.

The system:
BCA 7.5" 300 BLK upper, pistol length DE gas system
Aero Precision AR15 lower
Muzzle device: Witt machine SME (I intend to procure a suppressor via fed regulations eventually)
Odin works stainless adjustable gas block
Standard carbine buffer weight (~3oz) and spring (10.5" and 38 turns)
Ammo:Sellier and Bellot 300 ACC BLK 200grs/13.g (used on my 16" with zero issues) subsonics
barrel gas block hole is 0.109 stock

Test 1:
Gas block open 100 percent
Spent round ejects 50% of the time max - no double feeds
no lock back on last round
will not feed second round
Tried a pmag and hexmag - no change

Test 2:
Gas block open 100 percent
opened the barrel gas port to .141
Spent round ejects 100% - noticable increase in recoil
No lock back on last round
Will not feed secound round in mag
4 oz buffer swap made no difference

Test 3: (upcoming)
Close the gas block and slowly open - start over
Try a shorter spring
Try a lighter buffer

Suggestions? Thank you.

[FeuerFrei]

Recent thread about 300bo pistol may help you.

https://www.calguns.net/calgunforum/showthread.php?t=1819522

300bo in short pistol length proves to be a pain in the balls without a can. (subsonic loads)
Yes I know the link info is about a piston strap on kit.

[Old Flash]

Before going to a shorter spring, you could try a NEMO 300 BLACKOUT buffer spring. It's mainly designed for under gassed 16" carbines, but it helped me get my CMMG 8.5" 300 blackout running consistently with heavy subsonic rounds. FWIW, I'm using a heavy buffer and a Wolff extractor spring since I had some intermittent FTE's.

[sigstroker]

Some manufacturers assume anyone that gets a 7.5" Blackout is going to run a can on it and gas it accordingly. More backpressure with a can might make it operate better.

[sigstroker]

Also, try supers. They have a lot more muzzle energy.

[Angrysnarf]

Cool that you're reaching out to experts in CA

[sbo80]

I don't mean to be rude about it - but are you really sure that the block is open 100% and that the gas port hole is lined up correctly to the block? I have a 10.5" and even with subs and an H2 buffer I have my gas block dialed down and it still runs fine (I have a Superlative Arms block so it's "clicks", I have no idea what % it is, it's just not 100). I have no idea what my gas port hole is, it's whatever Faxon made it. I know 10.5 is a whole extra 3" of dwell time for pressure but it doesn't seem to me that would be enough of a difference between "runs at < 100% open" and "won't function at all".

[Wildcat19]

Before going to a shorter spring, you could try a NEMO 300 BLACKOUT buffer spring. It's mainly designed for under gassed 16" carbines, but it helped me get my CMMG 8.5" 300 blackout running consistently with heavy subsonic rounds. FWIW, I'm using a heavy buffer and a Wolff extractor spring since I had some intermittent FTE's.

Rog. Thx. I'll look in to.

[Wildcat19]

I don't mean to be rude about it - but are you really sure that the block is open 100% and that the gas port hole is lined up correctly to the block? I have a 10.5" and even with subs and an H2 buffer I have my gas block dialed down and it still runs fine (I have a Superlative Arms block so it's "clicks", I have no idea what % it is, it's just not 100). I have no idea what my gas port hole is, it's whatever Faxon made it. I know 10.5 is a whole extra 3" of dwell time for pressure but it doesn't seem to me that would be enough of a difference between "runs at < 100% open" and "won't function at all".

Thanks. Yes, I am really sure. I'm an engineer and ex-pilot. I own a micrometer, vernier caliper and other measuring devices. I believe another 3" is significant. But, will double check again.

[Wildcat19]

Cool that you're reaching out to experts in CA

Not just CA - many members have moved out of state and still frequent this forum.

[Wildcat19]

Also, try supers. They have a lot more muzzle energy.

Copy. I have some supers coming next week. Thx.

[Old Flash]

I don't mean to be rude about it - but are you really sure that the block is open 100% and that the gas port hole is lined up correctly to the block? I have a 10.5" and even with subs and an H2 buffer I have my gas block dialed down and it still runs fine (I have a Superlative Arms block so it's "clicks", I have no idea what % it is, it's just not 100). I have no idea what my gas port hole is, it's whatever Faxon made it. I know 10.5 is a whole extra 3" of dwell time for pressure but it doesn't seem to me that would be enough of a difference between "runs at < 100% open" and "won't function at all".

Thanks. Yes, I am really sure. I'm an engineer and ex-pilot. I own a micrometer, vernier caliper and other measuring devices. I believe another 3" is significant. But, will double check again.

I agree that the extra length will make a difference. After getting my 8.5" running, I built a 10.5" 300blkt and it functions 100% with subsonic rounds using original gas port size, pistol length gas tube, standard carbine buffer and spring, and GI mags.

Copy. I have some supers coming next week. Thx.

Super rounds should function, especially with that gas port size. Good thing you have an adjustable gas block.
I'd save the supersonic rounds for your 16" but that's just me.

[Wildcat19]

Yeah, I'd rather keep the pistol to subs. Supers already came - Sunday I'll continue testing the subs. Then adjust for the supers. Thanks.