Gas port diameter, 300BLK 8" barrel

[Tim K]

Test fired my new SBR today with some subsonic ammo a friend gave me. It's undergassed. The existing port measures 0.082" or so. I have a 0.097" drill, but I have no idea if that's too much. Should I try to get between those numbers?

8" barrel, pistol gas, suppressed.

[ray1970]

Interested in knowing. I have an 8" barrel on the way. I would love to know what size the port should be so that I can check it before I assemble it.

[J]

Grrr. I want to help... But mine runs so well I don't want to mess with it. But for sake of science I'll pull the hand guard and gas block tomorrow unless work keeps me late and let you know.

[skullybones]

If the diameter increase is that small, I'd ream instead of drill. Or sinker EDM for the ultimate no-burr experience. Give me a shout if you need anything.

Recommended size is out of my lane.

What is the hole size entering the gas block?

[KS63]

I pin gauged my port on a 16" barrel with carbine length system and its .109" checkout the 300Blackout Forums for more info.

[Hoser]

I will tear mine apart when I get home from work and check.

[MarkCO]

0.082" is likely going to be a tad on the small size for most set-ups. Mine that started 0.070" with a 10" barrel, I opened to 0.094" and it runs perfect. However, I have seen others that needed to go up to as much as 0.105". Your specific barrel geometry, load, gas block seal, suppressed or not and the BCG will all have an effect. If you have the load you want, then you can surely start to bump the gas port size. If you are purely going numerical drill sizes, open until you get lock back at least some of the time and go one more drill size. That should have you GTG even in the cold. I'd not base my decision off what someone else uses unless you have the exact same parts and load. We don't want all that extra gas if we can help it.

[Tim K]

I tried 0.093". It cycles but won't lock back the bolt. It's now at 0.097", but I haven't tried it yet.

[Tim K]

0.097" didn't work.

I tried 0.107" and it seems perfect. Ejection was still pretty gentle, throwing the brass 4-5 feet.

[ray1970]

Well, that was quite a jump up in port size. I'll be curious to see what size my port is right out of the box.