Not cycling with subs

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Re: Not cycling with subs

Post by dellet »

knj300blk wrote: Sun Jul 02, 2023 7:29 pm Based upon what I read AR makers are porting 300blk assuming you will be suppressing subsonics. That is a fair assumption. That said, an any barrel with a .075" gas port is not going to cycle subs unsuppressed. Suppressed it would've.
Not true. The system was designed to work in all 4 configurations. Sub/super, suppresses or not. If I remember correctly, the pistol gassed 16” barrels made by AAC were ported at .072”. I still have one and can double check that.

However, I am one one those weirdos that wants to shoot subs unsuppressed. Bases upon what i have read it doesnt happen consistently with a gas port less than .090". At .085" where i drilled out to, I am very close. As mentioned, ive gotten one brand of subs to cycle 100%.

The Aero precision adjustable gas block might be leaking. I took it apart and there is evidence this may be the case. I have superlative arms coming to try so i can rule that out before drill out. If the gas blocks ends up not being the issue, I am drilling out to .090" or .093" as a next step. I have kak, 3pc light buffer kit coming as well with 1.7,2.2 and 2.6 oz buffers to try as well.

I will get it to work, mark my words. I'll report back here with the final configuration.
By original design, full auto carrier, H2 buffer for pistol gas. Carbine gas is standard weight buffer
Port on my 16” carbine gas is .097”, operates fine with subs unsuppressed.12” pistol gas is .078” works fine. 10.2” carbine is equivalent to a .115” port will only shoot a few factory loads unsuppressed and a couple hand loads. By the book shouldn’t work at all.

This guy did extensive testing to sell his gas blocks, note that he had the wrong buffer when testing tha carbine gas system, too heavy. ... e-testing/

More than likely you have more problems than just the ammo.
300 Blackout, not just for sub-sonics.
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Re: Not cycling with subs

Post by rb288 »

Ok, I know this is a bit of an old thread, but I just had some experience with this problem.
My 8.25" SBR would NOT run subs at all.
Acted like it was undergassed.
190gr sub-x and 220gr hpbt, would shoot, be accurate, eject properly, but not load the next round.
With a single round, in the mag, it would eject and lock back properly.
Did all kinds of things to try to fix it, a lighter buffer spring, a lighter buffer, measured the gas port (.120"), lubed the heck out of it.
Nothing worked.
On a whim, I found a friend had a 300blk magazine so I tried it.
Boom, problem went away and it is running like a Swiss watch.
Anything over 180gr or so just doesn't seem to want to run in a standard 556 mag.
It's oversized profile gets hung up on the support ribs of the 556 mag.
So, if you are going to run heavy subs, get a dedicated 300blk mag, like from Lancer.
I may have been on the losing side, but, I'm not convinced it was the wrong side.
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