300BLK Subs at 9,300ft

[Tim K]

It's 8 or 8.5", I forget exactly.

[belizejet]

So.....my subs run great through my 16" barrel upper, even down to 10.6grn of AA1680. I think my next step is to replace my gas block with a standard one and/or tap the gas port out slightly larger. The pistol gas system vs the carbine system make a significant difference I guess.

[EricTheRed]

My first question would be what weight buffer are you using? Is a lighter one possible? If so that is probably a cheaper and easier test that messing with the barrel- in my experience port sizes and buffer weights are pretty closely tied together (all that has been 5.56 exp but I can't see why it would be conceptually different). Second would be if you have tried something like the JP low mass BCG, potentially in conjunction with lighter buffer. Third would be do you plan to run supers as well in the future? If so, I personally would hold off on opening the port AND changing the gas block (again due to my experience with 5.56 and under/over gassing issues between combos of subs/supers/suppressed/unsuppressed). From what little I know of your barrel (grain of salt and all that) some people have gone out to .125 on it to get it to function well. I believe it's .096ish originally iirc, but anyways I'd start small on opening it up. My 2cents.

Very curious to see what results you have as my can should be out of jail in a month or so and I'll start shooting my 9" AAC 300 with subs in earnest.

[belizejet]

I'm an idiot. I pulled the adjustable gas block off and was looking at it. I noticed the gas port was blocked with something that looked threaded. I thought the flush gas adjustment screw fell out and I had a replacement screw bought. Well.....the screw had worked it's way all the way in somehow instead. I was getting almost no gas and thought I was adjusting the gas with the new one. These are tiny screws. Long story short, I opened up the gas with the old screw, reset it, then shot it. My subs work fine in it so far. Live and learn. I shot 10.6 grn no problem and may go lower since they cycled fine.

[Tim K]

Glad you got it sorted out.