Tell me what I'm overlooking.

[26 Inf]

Gas Block Square and Plumb to Port?

Barrel came pre-dimpled. I installed gas block on the dimple and then drilled and pinned. Looks plumb.

Today I took the upper down and unpinned the gas block - you could see the outline of the much bigger gas block orifice around the port.

I measured the port size - the .074 pin went in with a little movement, the .075 pin wouldn't go in, so I'd guess you could call it .074 to .0745ish.

That is the first Geissele gas block I've unpinned after I've pinned them. I was really impressed with how nice the channel in the barrel looked. Went back together easy, I even re-loctited the allen screws, even though I was kind of wondering why I even re-installed them, LOL.

[26 Inf]

Check the gas key alignment if you have not. Marginal rings or a loose key would show up on a shoty middy but might run a 16" CAR gas.

Ran the old BCG drop test on it, rings are good, gas key shows no sign of leakage. Gas key/carrier sans bolt slid on and off key smoothly before I pinned gas key, still did after reassembly.

[26 Inf]

https://docs.google.com/spreadsheets...JXXrk/htmlview

Good info, but if you look you will see port sizes vary a good deal by who makes them (only a couple 13.7" ones but you can compare).

It's the A5 curse.....

I'm thinking it is port size. What hornswoogled me was the fact that it did finally function with the A5H3 buffer, even though it wouldn't lock back.

It makes no sense that it didn't function with the lighter A5 buffer, or the carbine buffers I tried when I switched lowers.

Oh, well, I see Noveske runs .087 and Triarc runs .073, so I'll start with .076 (#48 wire) if that doesn't work I'll go with .0785 (#47 wire) and if that doesn't work I'll go with .081 (#46 wire).

Just ordered them from McMaster Carr.

[26 Inf]

What brand barrel?

Prefer not to say until I've had a chance to talk with them.

[georgeib]

Prefer not to say until I've had a chance to talk with them.

You may want to talk with them before drilling the port.

For that matter, it may be worth checking the gas port to make sure it isn't obstructed somehow. Or the gas tube itself.

[MistWolf]

I'm thinking it is port size. What hornswoogled me was the fact that it did finally function with the A5H3 buffer, even though it wouldn't lock back.

It makes no sense that it didn't function with the lighter A5 buffer, or the carbine buffers I tried when I switched lowers.

Oh, well, I see Noveske runs .087 and Triarc runs .073, so I'll start with .076 (#48 wire) if that doesn't work I'll go with .0785 (#47 wire) and if that doesn't work I'll go with .081 (#46 wire).

Just ordered them from McMaster Carr.

No! Don't drill a thing until you've eliminated all other possibilities! Once you start opening up the gas port, you can't go back.

I remember when I started having trouble with an LMT Enhanced carrier equipped with a standard bolt. A lock back check verified the problem was short stroking. After a lengthy investigation (complicated by the fact the extractor spring was marginal and slowly failing) I discovered the gas key developed a leak and the gas tube knob that fits in the gas key was worn. (The rings were also worn, but that was discovered early on and the rings replaced.)

If (after a thorough investigation and all gas leaks have been eliminated, the barrel still short strokes) try it with a suppressor. It may be gassed just right for suppressor use.

(I'm not certain, but I believe a .071 to .073 gas port should be good for a middy.)

PS- The A5H3 buffer is heavier than needed. An A5H2 is the same weight as a rifle buffer which is optimal.

[Clint]

.0748" is a standard drill size (1.90mm), so that's probably what it is now.

Sometimes a brand new barrel can have a little bit of a sharp edge or burr on the gas port entrance that slows down the flow a little.

Some shooting usually smooths this out and increases gas drive slightly.

This may only be notable when the port is on the small side of the normal range, as it is in this case.

Try running a session with the A5H0 and perhaps some 5.56 ammo.

If that all goes well, then try the 223 range ammo again.

Today I took the upper down and unpinned the gas block - you could see the outline of the much bigger gas block orifice around the port.

I measured the port size - the .074 pin went in with a little movement, the .075 pin wouldn't go in, so I'd guess you could call it .074 to .0745ish.

That is the first Geissele gas block I've unpinned after I've pinned them. I was really impressed with how nice the channel in the barrel looked. Went back together easy, I even re-loctited the allen screws, even though I was kind of wondering why I even re-installed them, LOL.

[26 Inf]

Thanks guys!

I'll hold off.

MistWolf: Problem is that with the 13.7 I used a JP flash hider because of the length and shroud for pinning in barrel versus threads. So no suppressor mount.

ETA: It was 52 degrees yesterday, 19 degrees right now. It'll be a couple days before I hit the range again.

[ABNAK]

I'd be curious what some full-on 5.56mm NATO ammo would do in your setup as opposed to .223 pressure stuff. Never know, some barrel makers gas them specifically for 5.56 ammo, might wanna ask the manufacturer if that is the case (Hodge is one I can think of offhand).

[G.B.]

I have two BA Hanson barrels that Remington umc makes them single shots. It has worked fine in many other ars I’ve used it in. Every other 223 pressure ammo works fine. I just don’t shoot that one kind of ammo.