Gas Port Size Feedback

[BluntForceTrauma]

I'm wondering how the gas port sizes of my Faxon group buy barrels (as well as Alexander Arms barrels because they have the same port sizes) are feeling to you guys. Feedback on other barrels is also helpful if you happen to know the gas-port size.

How does the gas system of the various barrel lengths feel? Over-, under-, or just-right-gassed?

Ejection pattern can indicate gas level. How are ejection patterns with various kinds of ammo?

Short-stroking or lack of mag lock-back can indicate gas level. Any feedback here with various kinds of ammo?

I'm trying to fine-tune the gas-port sizes of my group buy barrels so they are soft- and smooth-shooting while functioning reliably with lower-power Wolf 65G steel-case and all other factory ammo.

[Crusty]

The gas port on my 18" Satern Liberty MLGS barrel is .093" and my rifle is way overgassed, to the point that I had to install an adjustable gas block to stop stovepipes because the BCG was already on the way back before the shell had cleared the receiver, even with an H2 buffer (but before the AGB). It cycled Wolf without problems (lower pressure) but I had stovepipes with any Hornady ammo, and since I want to hit stuff smaller than paper plates I need it to handle premium ammo reliably.

I did have an extractor with sharp points hanging onto shells that was a part of the problem, but still my action cycled crazy fast when there was no need for that kind of speed in a semi-auto rifle.

[ALshooter]

My 20" group buy bbl cycles fine and ejects at about 4 o'clock but does not lock back on empty. I've only put about 30 rounds through it so far so it could be a small GB leak that's not sealed up yet. Time will tell. I'm fine with it though because this gun will be shot through my Form 1 suppressor 95% of the time once my stamp comes back.

[BluntForceTrauma]

Crusty, per Bill Alexander, the gas ports on my F18 mid-lengths are 0.076".

ALS, gas port on the F20 rifle-lengths is 0.093", so "should" be OK. Let's keep an eye on it as it breaks in. This is a complicated thing because it also depends on ammo variables, buffer weights, build quality and parts fit, lube regimen, etc.

[Crusty]

Bill's right (the source after all) but I have found other references online which indicate that .093" is within spec. But it's too much gas. I sometimes wonder if there's a bunch of manufacturers out there making up Grendel specs as they want them to be.

[bj139]

I had to look back to see what I posted in the 20" group buy thread.
I said there were a few bolt over base conditions.
Also, the bolt never locked open on an empty mag.
Doesn't bolt over base mean over gassing and not locking open on an empty mag mean undergassing?
If so, then I guess on average, it is just right.

[StoneHendge]

I had to look back to see what I posted in the 20" group buy thread.
I said there were a few bolt over base conditions.
Also, the bolt never locked open on an empty mag.
Doesn't bolt over base mean over gassing and not locking open on an empty mag mean undergassing?
If so, then I guess on average, it is just right.

Not locking open can also be overgassing if there is too force on the way back for the bolt to catch

[BluntForceTrauma]

BJ139, what ammo and did you happen to notice anything with ejection pattern?

[sneaky one]

BFT, when we measured the 16" F tubes, were they the same as the 18", at .076, ? IIRC, they were.

[VASCAR2]

Sneaky I wouldn’t be surprised the 16” Faxon GB and 18” Faxon BG used the same gas port diameter. I’m just going by how both shoot, ejection pattern and recoil. I didn’t measure either gas port but I’ve had no reason to want an adjustable gas block on either, but I don’t use suppressors.

I’ve only shot 29 rounds in my 18” GB Faxon with temperatures between 10 and 20 degrees. I kept my ammunition warm and ejection was 3-4 O clock.

[monty]

According to Ballistic Advantage tech support they use an .067 gas port on their 16" Hanson barrel.

I recently built an upper with that barrel. Noticed that the gas port looked small when building. BA includes a gas block that is pre-drilled for a pin which I used. After assembling and test firing with a single bullet, the bolt would not lock back all the way. Usually would catch the top of the magazine. Empty cases just kind of dribbled out. Many would be laying a few inches away on the bench. Seems way under-gassed to me. But BA says there have not many problems with them. They have my upper now, so hopefully this will be working soon. I will update if there is any new info from BA regarding gas port sizing.

[sneaky one]

Vascar, I contacted L 52 as we checked the ports - in my basement , as BFt was here with the first 10 samples of F 16" bbls. An exciting moment for us both here.

Yes, it was confirmed thru L 52 that anything mid to high .075 issh is good. I do have an excellent memory, I just have to find that day in my memory. No, I'm not that old yet..

My wife has almost the same photographic memory from her Dad- I studied them both on how to memorize many things in ones life- daily. Fascinating study.

Anyway, the F16" tube is a rockstar for me. It's waiting for a low cost, used once per year- muffler.. Rebel fits the bill for me...

F-16, F-18" sounds cool for the Faxon tubes - right? F12, etc. F 20" is the howitzer tube. A 24" is the cruise missile launcher! No offense to the snipers on here. Bill W has a 28" rifle tube.

[BluntForceTrauma]

Port on the F16s, again per Bill, is 0.078", just a bit bigger than F18 of 0.076".

[bj139]

BJ139, what ammo and did you happen to notice anything with ejection pattern?

It was Wolf steel cased ammo and they ejected at around 4 o'clock.

[grayfox]

I have the 18" group buy faxon, and also a faxon gunner 16"... I measured both ports and they come to [edited] 0.078-9 +/- 0.001, with my calipers. Now there could be a small measurement uncertainty b/c I was measuring to the edges of the port not the actual hole... anyway they both seem to be close to the [edited] 0.075" ref'd above. Shooting wise most of the time I've had a brass catcher on but other times the few I did uncatcher-ed seemed to smack back about 4 o'clock... Note however that those had a good ding in the case mouth... remedied by the little velcro trick. Hope this info is some help.

I'm going to tune my AGB to help ejection... this is my first AGB tuning.

[kcb38]

But BA says there have not many problems with them. They have my upper now, so hopefully this will be working soon. I will update if there is any new info from BA regarding gas port sizing.

They're starting to get complaints on AR15.com. They seem to be willing to work with the customers to make them right though. I'll be interested to hear the outcome of your situation.

[monty]

BA called on Monday about this. They said it worked perfectly for them. Then they said that they had changed the gas tube because it "did not look right". They are shipping it back to me, so we will see if it is working now.

Got a link for the thread on ar15.com?

[Crusty]

Most machinists use a complete drill index to gauge small holes because calipers are prone to measurement errors. Find the last bit that will fit in the hole (use the smooth end) and the first one that doesn't fit and you've gauged a hole measurement within an acceptable range of tolerance.

I couldn't do my own work without a drill bit index (plus a tap and die set) so I've got them on hand to use. Always tighten drill your chucks adequately so that the bits don't spin and get marred, which will ruin them for gauging purposes.

[kcb38]

Monty I first saw mention of it at the end of this thread , saw a couple more in the BA subforum and also a few in the "variants" subforum. Poking around the interwebz I found a few more examples of BA barrels being under gassed as well. Not enough to think it's a widespread issue, but enough to see it wasn't an isolated incident either. Some of the issues seemed to be fixed by swapping in a lighter buffer and some weren't.

[tracker12]

I have a box thru the 18" group buy. The gun has functioned perfectly. Ejections and feeds were flawless and gun recoil and rebound very smooth.