I have a problem with gas - Pics added to help

[runway1]

Randall, Harrison from ARP says the load used (28.5 gr w/110 BTHP) runs at 58K. That is not over pressure. I've been using this load for several years now in a Bison 16" barrel as well with no adverse pressure indications. Brass in this ARP barrel also shows no adverse pressure indications.

Whatever the problem turns out to be, it isn't the load.

[ar15barrels]

How did the short-stroke test go?

[runway1]

I'm itching to do that but I have this job thing that puts a damper right in the middle of the day! Starting to irritate me.

I have a box of factory Hornady 110g and a new gas tube, just in case. I don't think I can get to that test for about a week...but I will and then I'll get back.

Also, really appreciate all the inputs. Very smart and helpful, many thanks.

[freebug]

I had a similar dilema with one of my builds where the barrel anticipated the presence of a handguard cap. From your picture, there's no space for it. My barrel is a BCM hammer forged and I needed to leave some space for where the handguard cap thickness should have been.

That's why the toothpick solution works. You know the holes are aligned. Right now, you have it set all the way back and assume the holes are aligned but don't really know.

[runway1]

I don't have a handguard cap. Not sure what you're saying. Regardless, the picture clearly shows the telltale ( gas mark off) of aligned holes.

[runway1]

How did the short-stroke test go?

Well, it short stroked just fine. Using Hornady 110g. First shot teased me - it locked open. I thought...cool, it's an ammo problem.

I loaded two for a back to back and then lock open - nope. Went back to one for a lock open - nope. Tried my ammo - nope. Back to the Hornady ammo - nope. All short stroking

[PMACA_MFG]

There should be a small gap where the gas block butts up against the barrel to accommodate for the front handguard retainer, so it may not be aligned with the barrels gas port. By hand use a small drill bit to clean out any shavings that be left in the gas port.
Also EBay and Amazon are probably the second worst place to get parts for with gun shows beating them out by a very slim margin.

+1.
If the gas block is for a handguard set up and you put it on a free float rifle, the hand guard cap disappears and the gas block mounts 1/16" closer to the chamber.

[arnie19]

The stain on the barrel from gas shows the block is located ok.You need to open the port or try a slower powder after you confirm that the bolt locks back when charging by hand and has about 1/8 inch or more play before the bolt head hits the bolt stop. You might also have a too heavy buffer or spring .I had one rifle that wouldn't lock back because I had a finger activated bolt release and I think it was too heavy to keep up with the speed of the bolt .

[runway1]

The stain on the barrel from gas shows the block is located ok.You need to open the port or try a slower powder after you confirm that the bolt locks back when charging by hand and has about 1/8 inch or more play before the bolt head hits the bolt stop. You might also have a too heavy buffer or spring .I had one rifle that wouldn't lock back because I had a finger activated bolt release and I think it was too heavy to keep up with the speed of the bolt .

Mentioned in earlier posts:
Slower powder.....Hornady factory ammo has same result

Heavy buffer spring.....behaves the same with other lowers that have worked fine for some time.

Head space is fine.

[runway1]

+1.
If the gas block is for a handguard set up and you put it on a free float rifle, the hand guard cap disappears and the gas block mounts 1/16" closer to the chamber.

And this would cause...???

Block is correctly aligned and demonstrated by measurement and visual mark off.

[runway1]

That's why the toothpick solution works. You know the holes are aligned. Right now, you have it set all the way back and assume the holes are aligned but don't really know.

I did the toothpick test with a 1/16 Dia steel rod I snipped off. Fell right through easily. So now we have measuremnt, mark off and toothpick test. Block is correctly aligned. I can eliminate that.

[PMACA_MFG]

And this would cause...???

Block is correctly aligned and demonstrated by measurement and visual mark off.

From what I see the hole in the gas block is not centered over the gas port. But if its as big as the mark would have us believe then it should be OK. How loose is the gas tube in the gas block?

[runway1]

No play in the gas tube. It's in there well. Pin is tight.

[ar15barrels]

I'll just leave this earlier quote here:

Assuming it fails the short stroke test and you don't have an obvious gas port burr blocking the gas port, you have two easy options.
Switch to a slower powder to increase gas port pressure or open the gas port diameter to increase gas flow.

[runway1]

I'll just leave this earlier quote here:

Well, given the factory ammo had the same result, that statement leaves me at opening the gas port, right?

I think I'll contact ARP. How could one of the industry leading barrel makers make a barrel that needs a larger port? Also, the port dia seems industry nominal. Strange.