Gas Port Size for 12" unsupressed barrels?

[sharpshooter33]

So I've just gotten a 12" barrel, assembled it today verified the gas block was aligned correctly. Everything looked good...
Took it out for test fire and the BCG would not LRHO. I fired 2 mags with 1 round and they would hang on the magazine but not fully engaging the bolt stop. I fired a mage with 3 rounds and had to hand cycle each one. It would recock the trigger, but not strip the round.

So I'm wondering does anyone know the minimum gas port size to function a CAR length gas system on a 12" barrel?
I was using under power wolf ammo for the test firing.
Don't really wanna say who the manufacturer is yet because don't want to be knocking a good barrel company, but I had the same problem with a 300BO 7.5" made by them. They did great at opening the port up for nothing, but I wanna be sure I'm not talking outta my butt when I start addressing the issue if it is an undersized gas port.

Thanks for any input.
SS33

[grayfox]

Could be everything is still stiff or as stated, the Wolf being underpowered.
From an earlier thread by one of our solid resources (Lrrpf52) here is what he wrote on gas port sizes:

Quote:
General speaking, if going off of Bill Alexander's extensive developmental work on setting up gas ports:
20" RLGS .0935" (like on a 5.56)
18" MLGS .076"
16" MLGS .076"
16" CLGS .0625"
My Faxon 12" CLGS group buy is .068", runs great suppressed and unsuppressed so far.
These barrels and ports will generally drop onto an existing lower whether it has a carbine RET, 2.0 ounce buffer, and Mil-Std carbine spring or a rifle RET/spring/5.1 ounce buffer.

This might give you something to go on.

[VASCAR2]

There have been many reports of Ballistic Advantage 12.5” barrels being under gassed because the gas ports were to small. BA assumed most users would use suppressors and tend to be under gassed without a suppressor. The Faxon 12” Group Buy barrels with carbine length gas port were .068”. I’ve read where some BA owners used .070” or a little larger port to get reliable functioning without a can.

Temperature and ammo can contribute to short cycling with a new upper. After the upper wears in your gas port might be gtg. I think I’d try some other factory ammo before I pulled the gas block. You can use drill bits to get pretty good measurements on size of the port if you don’t have calipers.

[wideglidejoe]

There have been many reports of Ballistic Advantage 12.5” barrels being under gassed because the gas ports were to small. BA assumed most users would use suppressors and tend to be under gassed without a suppressor. The Faxon 12” Group Buy barrels with carbine length gas port were .068”. I’ve read where some BA owners used .070” or a little larger port to get reliable functioning without a can.

Temperature and ammo can contribute to short cycling with a new upper. After the upper wears in your gas port might be gtg. I think I’d try some other factory ammo before I pulled the gas block. You can use drill bits to get pretty good measurements on size of the port if you don’t have calipers.

I have a 12.5" BA barrel, with the same issues you stated sharpshooter33. I called BA, they told me the same thing VASCAR2 said, they assumed it would be used w/suppressor. They said my barrel should have left the factory with a .055" port, I measured it as .050", I drilled it to .073" and it runs great w/o a suppressor.

[sharpshooter33]

Ok, interesting .068 on the Faxon. That's what I have. A 12" Faxon barrel. I had an issue with a 7.5" 300BO barrel, but they immediately took it back and fixed it. They also planned on the 300BO shooters shooting suppressed.

Interesting that Greyfox has had no issue from his. I have a NiB BCG so it's slick shouldn't be much to break-in. it was cold around 40 degrees and I used Wolf ammo, I was going to shoot 5 more today but didn't get around to it. I'll do it tomorrow.

The 7.5" 300BO needed to be opened up to .098 to function subs and supers unsupressed.
I was thinking a 12" would need somewhere around .085, but if Greyfox is getting reliable function with .068
I usually run an H3 buffer in my CLBS. I'm not sure what is in mine right now. It may be standard CAR on the pistol lower I was using. It's a spare that I don't usually use much.
what is RET? Rifle Extention tube?

Grey have you used Wolf in your Faxon 12?

[grayfox]

No I didn't shoot any wolf (my indoor range doesn't allow), and I had a standard wt buffer by the way, 12.5 BA barrel.
Hornady custom, Black and Federal 90 gr AE.
It was Lrrpf52 who measured his faxon at 0.068 (I quoted his post).
My shortie was a BA (I've since moved on, not really liking the short style).

[VASCAR2]

In the group buy section BFT has state 12” GB Faxon and Green Mountain 12” 6.5 Grendel barrels use carbine length gas port at .068 inches.


Colder weather does tend to decrease velocity/pressure but I have shot my PSA 12” nitride at near zero degrees with Wolf 100 grain FMJ steel cased ammo. I read where PSA used .068-.070 inch gas port but I haven’t measured mine. My 12” uses the supplied carbine buffer and spring with a SBA3 pistol brace but PSA 12 inch 6.5 Grendel comes with an adjustable gas block. My pistol has functioned 100% out the box without any adjustments to the AGB.

[LRRPF52]

So I've just gotten a 12" barrel, assembled it today verified the gas block was aligned correctly. Everything looked good...
Took it out for test fire and the BCG would not LRHO. I fired 2 mags with 1 round and they would hang on the magazine but not fully engaging the bolt stop. I fired a mage with 3 rounds and had to hand cycle each one. It would recock the trigger, but not strip the round.

So I'm wondering does anyone know the minimum gas port size to function a CAR length gas system on a 12" barrel?
I was using under power wolf ammo for the test firing.
Don't really wanna say who the manufacturer is yet because don't want to be knocking a good barrel company, but I had the same problem with a 300BO 7.5" made by them. They did great at opening the port up for nothing, but I wanna be sure I'm not talking outta my butt when I start addressing the issue if it is an undersized gas port.

Thanks for any input.
SS33

How did you install your gas block and how did the block fit to the journal on the barrel?

If it was a slip-fit, there might be gas leakage.

A .068" port should run fine with most ammo.

I did notice that 90gr Federal TNT would not cycle fully unsuppressed when using the stiff Maxim Defense short recoil spring that comes with their PDW brace and tiny buffer.

As soon as I attached the ThunderBeast Ultra 5 .30 cal can, it ran like a raped ape, even with the Bootleg adjustable gas bolt carrier turned to the suppressed position IIRC.

[sharpshooter33]

I took it all apart after running a total of 13 rds thru it. Every single load mag after taking the gas block off and checking to make sure it was centered would lock on the BCG and not the bolt face. it would eject the round a 3 o'clock. It would not cycle enough to strip the next round off on double mag loads. All was with Wolf ammo. it might cycle something else, but why try. I took it apart and did a rough check of the port size, by drill bit. The size looks to be around .073 ish. .078 would not go in.
The port markings show the gas port and gas block were perfectly aligned. No dragging on the BCG or the CH. Action feels smooth. My 12" PSA has no problems cycling Wolf ammo same batch of ammo.
LRRP... I'm running a standard CAR buffer and spring. Checked that also.
gas tube is Brownells standard CAR buffer tube. Gas block is a slide on LP. It didn't show any signs of leakage of gas when I disassembled it.
fit of the gas block is snug. I have to work it on and off. lock down is good. BCG is a Toolcraft NiB properly staked and no signs of leakage there.
hmmmm. I have no where to look other than the gas port size.

[grayfox]

I wouldn't judge the setup based on how it handles wolf ammo. Shoot some regular factory in it, some 120-123 loads like Hornady, federal or good quality ammo.
After about 50-60 break in rounds of that then go back to the wolf and see how it does.

[Kswhitetails]

GF - in my experience if it doesn't cycle the Wolf steel, it won't cycle much. I'm not sure if it's a do all test bed, but the steel definitely has the pressure and volume to cycle a properly laid out action. It's just me, but I think many of these builds seem to run with issues (my experience included) until at about 50-60 rounds. Then, for some reason, they're magically better. I have a feeling it's because many of the parts are so new that the finishes on the metal on metal contact locations need some wear to break in the "slip". Dunno, but I've read so many threads over the last two years from guys all encountering the same issues, then they seem to vanish after the fourth or fifth mag of ammunition, never to be heard from again. It's almost like once the issue goes away, so do they...

[sharpshooter33]

Well I did discover something this week. I put 1 round of Hornady Black in it and took it out back and fired it. Locked back just fine.
I'm thinking it's a combination of things. .073 gas port, under power wolf with steel case that doesn't seal well, with a 100gr pill and all parts are new. Also cooler temperature here.
Interesting that the Hornady did get LRHO and even dented the brass off the deflector.

I agree with you Kswhitetails, my expectation is that it should function the crap wolf ammo as a base line. I'm going to cycle some Hornady Black thru it and then come back to this issue. Functional to me is it will function on the wolf ammo even though I won't use it for anything but plinking with wolf, but it should function with it.

GF - in my experience if it doesn't cycle the Wolf steel, it won't cycle much. I'm not sure if it's a do all test bed, but the steel definitely has the pressure and volume to cycle a properly laid out action. It's just me, but I think many of these builds seem to run with issues (my experience included) until at about 50-60 rounds. Then, for some reason, they're magically better. I have a feeling it's because many of the parts are so new that the finishes on the metal on metal contact locations need some wear to break in the "slip". Dunno, but I've read so many threads over the last two years from guys all encountering the same issues, then they seem to vanish after the fourth or fifth mag of ammunition, never to be heard from again. It's almost like once the issue goes away, so do they...

[A5BLASTER]

Open up the rifle and lube the bcg, charging handle soaking wet and run it by hand bout 200 times.

That should break it in.

[LRRPF52]

I was going to ask you want temps you were shooting in next.

With Wolf 100gr steel case and low temps, looks like there isn't enough back pressure to cycle the action.

If your port is .073", it's slightly on the large side.

What type of rifling does the barrel have? My guess is it isn't Enfield rifling.

[sharpshooter33]

Faxon 5R rifling. 1:8 twist.
So out of activation u ran 1 round of Hornady black thru it and perfect function. Even dinged the brass mouth on the deflector.
I was surprised that there is that much difference in pressure.
Made me feel better about the barrel port, but still I think a barrel should function with any ammo.
Temp was around 45-50 degrees