Gas port size for 11.5 inch AR.

[aaholland]

What size gas port is needed for a always suppressed 11.5 inch carbine gas barrel? I would rather not need an adjustable gas block. This will be in an AR.

I am ordering a PF 6.5 Grendel Criterion Barrel. Percision Firearms says they can drill the gas port to any size. But they recommended .90 for suppressed only use. Doesn't that seem big? I though I would want smaller for suppressed use.

[Bigs28]

I would trust that mark recommends. Adjustable gas blocks are cheap though. Not sure why you wouldn't want one.

[aaholland]

I would trust that mark recommends. Adjustable gas blocks are cheap though. Not sure why you wouldn't want one.

One less part to fail. I only shoot suppressed and will be using the same grain bullets.

[aaholland]

From my net searches 12 inch barrels range from .067 to .075 at carbine length.

So .060 should be a starting point I would think?

[aaholland]

I contacted faxon their 12 inch is specked to have a .073 gas port.

I dont mind "tuning" the gas port size after I get the gun build I just need a starting point.

[Kswhitetails]

A few resources here that would be better than most, especially LRRPF52. If he says it, it’s got real knowing behind it. First blush from my weak eyes says you may be right, .90 sounds large for a short suppressed only build to me. 52 would know if that’s wrong, and better, would know why.

[LRRPF52]

From my net searches 12 inch barrels range from .067 to .075 at carbine length.

So .060 should be a starting point I would think?

If shooting unsuppressed with an 11.5", you need a larger port than you would on a 12.5" because of plug dwell time and bore volume.

A number of variables come into play when shooting suppressed:

* Diameter of the suppressor baffles (is it cut oversize for .30 cal or 6.5mm?)
* Length of the suppressor (longer suppressor generally mates better with smaller port, shorter suppressor with larger port)
* What type of chamber you have
* Action spring weight/strength
* Buffer weight

I highly recommend the Bootleg Adjustable Gas Carrier either way, instead of messing with an adjustable block.

My 12" Faxon group buy barrel has a .068" port and cycles everything I've fed it suppressed, with it being better with the Bootleg carrier set to the suppressed position.

It's only .5" different between an 11.5" barrel, so it's a good data point for reference.

SAAMI chamber
.068" port
Ultra 5 .30 cal TBAC suppressor
Maxim Pistol Brace action spring and mini buffer (2.9oz)
Bootleg carrier
Gas tube is bedded

Ammo fired so far:

90gr TNT (won't cycle unsuppressed, 100% so far suppressed)
120gr Federal AE Match
123gr Hornady American Gunner

What suppressor will you be using?

[aaholland]

If shooting unsuppressed with an 11.5", you need a large port than you would on a 12.5" because of plug dwell time and bore volume.

A number of variables come into play when shooting suppressed:

* Diameter of the suppressor baffles (is it cut oversize for .30 cal or 6.5mm?)
* Length of the suppressor (longer suppressor generally mates better with smaller port, shorter suppressor with larger port)
* What type of chamber you have
* Action spring weight/strength
* Buffer weight

I highly recommend the Bootleg Adjustable Gas Carrier either way, instead of messing with an adjustable block.

My 12" Faxon group buy barrel has a .068" port and cycles everything I've fed it suppressed, with it being better with the Bootleg carrier set to the suppressed position.

It's only .5" different between an 11.5" barrel, so it's a good data point for reference.

SAAMI chamber
.068" port
Ultra 5 .30 cal TBAC suppressor
Maxim Pistol Brace action spring and mini buffer (2.9oz)
Bootleg carrier
Gas tube is bedded

Ammo fired so far:

90gr TNT (won't cycle unsuppressed, 100% so far suppressed)
120gr Federal AE Match
123gr Hornady American Gunner

What suppressor will you be using?

I will only be shooting suppressed. I agree if I somehow end up with it being overgased I will get an adjustable BCG. I just want to see if I can get the gas port correctly drilled then no need for adjustable anything.

I have a JP silent capture spring with the standard spring. I think it is a type 2 chamber in the PF barrel I am ordering. I got the JP enhanced bolt in a fail zero BCG. Suppressor stats are below.

Gemtech Dagger
Caliber: .300 WIN MAG
Diameter: 1.5"
Length: 8.8"
Weivht: 15.2 oz.
5/8-24 (2A) Threads
Material: Titanium