Switchblock Gas port Diameters for 300 Whisper/Blackout ???

[Shamrock-MP]

So what is the optimal gas port diameter for a 16" barrel with carbine length gas? .105-110"?

[Dolomite_Supafly]

If you want the most flexibility you need to have a pistol length gas system.

I can shoot 240 grain cast bullets down below 800 fps and have them cycle and lock back on an empty magazine. I can also shoot 180 grain bullets at subsonic velocities and have it cycle like it should. You are not going to find a single carbine length gas system that is capable of the same. At least not without a lot of tweaking like removing weights from the buffer and a lightweight buffer spring. And when you do this then you are going to have issues with bolt overspeed when you do.

I have yet to figure out why people are so against having a switch so the gun runs optimally.

I had a freind out this week and we tried every single powder I had with 240 grain cast bullets. None, I repeat none, of the loads were able to lock back on an empty magazine below the speed of sound. His port was drilled at .120" and the gas block was centered correctly. Everything was correct except his gun would not cycle any subs, including the factory recipe in the AAC website. It was well lubed and cycled supers perfectly.

Dolomite

[Shamrock-MP]

Thanks.

[-k-]

Everything was correct except his gun would not cycle any subs, including the factory recipe in the AAC website. It was well lubed and cycled supers perfectly.

There is some mechanical problem that is causing just enough drag or gas loss to make subs not function.

[Rumph]

I had a freind out this week and we tried every single powder I had with 240 grain cast bullets. None, I repeat none, of the loads were able to lock back on an empty magazine below the speed of sound. His port was drilled at .120" and the gas block was centered correctly. Everything was correct except his gun would not cycle any subs, including the factory recipe in the AAC website. It was well lubed and cycled supers perfectly.

Dolomite

For what its worth, here are a few other things to check:

Gas rings worn out?
Charging handle bent?
Gas tube obstructed?
Bolt carrier gas tube obstructed?
Good seal at gas block?
Weight of BCG? Should be pretty close to 10 oz.
Recoil Spring? Should be standard carbine spring - 10-10.5" and 37-39 coils.
Buffer weight? Should be standard carbine buffer - about 3 oz.

[Dolomite_Supafly]

I had a freind out this week and we tried every single powder I had with 240 grain cast bullets. None, I repeat none, of the loads were able to lock back on an empty magazine below the speed of sound. His port was drilled at .120" and the gas block was centered correctly. Everything was correct except his gun would not cycle any subs, including the factory recipe in the AAC website. It was well lubed and cycled supers perfectly.

Dolomite

For what its worth, here are a few other things to check:

Gas rings worn out?
Charging handle bent?
Gas tube obstructed?
Bolt carrier gas tube obstructed?
Good seal at gas block?
Weight of BCG? Should be pretty close to 10 oz.
Recoil Spring? Should be standard carbine spring - 10-10.5" and 37-39 coils.
Buffer weight? Should be standard carbine buffer - about 3 oz.

100% brand new build with only supersonics fired for function/break in. We even swapped lowers between his and mine. It still didn't function as it should. I tore the gun all the way down to verify port size and location. I also checked the gas block for obstructions.

By function I mean lock back on empty magazines. It may have cycled and picked up the next round but if it doesn't lock back on an empty magazine it is malfunctioning in my eyes.

He has a suppressor coming. Hopefully, which I think it will, it will work properly with a suppressor in place.

Dolomite

[Rumph]

I agree, it should lock back. The suppressor will undoubtedly increase the gas pressure, but I like a rifle to function with or without suppressor. I don't have any other ideas as to why it won't run. I have zero experience with cast bullets in ARs, so I don't know how that might be affecting the situation. You mentioned the rifle is new - maybe a little break-in will help.

[-k-]

100% brand new

I always recommend trying a known good carrier for malfunction diagnosis.

[SifuGun]

I have a Wilson Combat 16" barrel, and if I recall correctly, the gas port is .107 (but don't quote me on that), regardless, it's unmodified, and I shoot only supersonic rounds, all so far have been 147g slugs using 18 - 18.4g of A1680 . I have not had any issues at all with cycling, or hard cycling, actually, I have had a few, maybe 4 total failures to cycle (out of 300+ rounds, hence the reason of upping the powder charge). N adjustable gas block is probably a good idea if itsn the budget, I have a Blackfox Research "Cliq Block" on a 5.56 rifle, and it works fantastic for minimizing the unnecessary gas pressure in a carbine. I can use the standard mid length buffer assembly and still get perfect cycling.

If I were able to have SBRs and/or suppresors here in Cali, I would have run a Cliq block on the 300 as well just for the ease of tuning, someof the budget permits, it certainly couldn't hurt. Wilson claims that their barrels will work for both super and sub sonic ammo without any mods, so something to maybe consider barrel purchase wise, if they ever come back in stock.

I bought a 16" carbine gas SI barrel from Midways. The port size was .075" or so. I had to drill it out to .108" or 7/64" drill bit. So it would cycle super loads. I have tried all combinations of subs except A1680 powder. But went ahead and drilled out port to .125" And from reading others experience this should do the trick for all sub loads. I also think there will be no need for a adjustable gas block. As other have reported the extra gas from supers is barely noticeable. I hope it works will let You know after further testing.

[SifuGun]

Hey Guys, Sorry didn't get back right away with follow up. Just got email reminding i posted info about 300 blackout gas port. I very happy to report It worked awesome. Drilling out the gas port
to .125" solved the issue of cycling subsonic rounds in a carbine gas 16" blackout barrel. And you don't need a adjustable gas block or other nonsense. All standard ar 15 556 stuff, switch barrel make sure gas port is .125" if you want to cycle subs. And let it rock. Thanks see you out there shooting, but not at each other, lol.