Gas port sizing

[Junkie]

I picked up a retro upper, slickside, A1 handguards, 3 prong that I want to convert into something more like a 605 (although it's getting an RRA Entry stock for now, maybe a 607 later if I can figure that out for a reasonable price).

It has an A2 profile barrel on it, which really doesn't match, and it's a Del-Ton 1/9 barrel so I don't have much use for it... so why not cut it down to 16.5" or so. Most of what I shoot is Wolf Gold, I'm not planning on shooting steel case through it. I haven't cut down a semiauto rifle barrel before, or threaded one, so I figure I should start with one I don't really care about - if I screw it up it isn't a huge loss.

How big should the gas port be to run reliably?

[Locutus]

I picked up a retro upper, slickside, A1 handguards, 3 prong that I want to convert into something more like a 605 (although it's getting an RRA Entry stock for now, maybe a 607 later if I can figure that out for a reasonable price).

It has an A2 profile barrel on it, which really doesn't match, and it's a Del-Ton 1/9 barrel so I don't have much use for it... so why not cut it down to 16.5" or so. Most of what I shoot is Wolf Gold, I'm not planning on shooting steel case through it. I haven't cut down a semiauto rifle barrel before, or threaded one, so I figure I should start with one I don't really care about - if I screw it up it isn't a huge loss.

How big should the gas port be to run reliably?


The ink on my armorer certification is still wet and they still haven't printed my engineering degree, so take what I say with a grain of salt.

You make no mention of whether your intend to plug the rifle-length gas port and drill a new one at mid or carbine length or if you simply intend to enlarge the existing vent. If the latter, then you'll need to factor in the reduced dwell time...

[Junkie]

I'm planning on sticking with rifle length gas system. I know it's somewhat tricky to make a 16.5" rifle gassed gun run reliably, which is why I'm asking.

[pezboy]

I believe .110" is close but starting around .100" and slowly move up until it functions wouldn't be a bad idea.

[Clint]

That's in the ball park.

Just be aware that 16.5" rifle is not a very good gas system combination.

[Junkie]

I know it's tricky to make work well, but I've read great things about the VooDoo 16.5" rifle gassed barrel so it's possible.

I might go a hair longer instead (17" maybe) if it makes tuning easier.

[markm]

I had an instructor who did this to a Colt barrel no one wanted. He had good luck a .0900" I'd definitely start on the low end. Nothing sucks more than too much gas.

[Junkie]

I'd be much less inclined to do this if it was a Colt barrel.

[pezboy]

I had an instructor who did this to a Colt barrel no one wanted. He had good luck a .0900" I'd definitely start on the low end. Nothing sucks more than too much gas.

The 20" gas port is already larger than .090".

[Clint]

Yes,

reports of cutting down rifles to ~16" vary wildly

from
"it runs with the factory port size (.092-.093)"
to
"Had to open it up to .110 to get it to run"
to
"It worked at first but eventually quit working when dirty and needed the worn gas tube replaced"


Let us know how your experience goes.

[markm]

The 20" gas port is already larger than .090".

Wow. Really? I've never had to mess with a rifle port on my own.

Hmmm... maybe my brain remembered it wrong. Perhaps he was .099". It has been many years, and this was before I was correct-gas obsessed.

[Iraqgunz]

MK12 port size is .0995. 20" MILSPEC barrel is .093.