Understanding pressure curve and gas block setup

[bobke]

Need considered wisdom, please. Have new barrel and upper and to make short story shorter, am ejecting factory Hornady 123's without issue, but loads of 123 AMax and 28.35 of 8208, 31.35 CFE and 29.5 TAC and 107 Sierra will either fire and not extract or will extract, but short strokes and won't pick up next round. Hornady is no issue. Have LMT auto bcg and lightest buffer and carbine spring. Feel like I'm under gassed, but my other two Grendels have adjustable gas blocks and this one is fixed and about a .81-.82 gas port hole. Barrel shoots well, but mostly one round at a time. I can load a bit hotter, but am getting near where other barrels are near max with same loads. Do I need to have gas port bumped up and get an adjustable block? Are pressure curves of these loads just far enough short of an amount of gas necessary to fully function action-they are within 25-30 fps of factory loads, but coming up short of reliable function. Again, ya'll's wisdom and guidance appreciated.

[Drifter]

Describe your setup, such as gas system length, barrel length, gas block, etc. Is this a self build, or work done by someone else?

[bobke]

20" barrel with rifle length gas and non adjustable gas block. Professionally built and assembled.

[LRRPF52]

Try a heavier buffer, starting with an H2. Those loads have more than enough gas to run your system reliably. Your lightweight buffer is probably letting the carrier move back too quickly, which vents the gas out of the side of the carrier via 2 holes, hence the short-stroking.

I wouldn't mess with your gas port at all.

[bobke]

I had started with H3 and Tubb flat spring, then H2, then lightest buffer I had and carbine spring and then it began ejecting properly, but that was first pass at range. Went back today with loads mentioned and had short stroking issue, but not with Hornady factory loads, which shot with very good accuracy, as we've come to expect. These same handloads shoot and eject without issue from both other Grendels, hence my head scratching. When rounds eject, they're dropping out at around 4 o'clock in neat pile, so appears ejector and extractor are working properly, when allowed.

[montana]

I have a 18 inch barrel that had ejection problems similar to yours. I thought it may be under gassed , but ended up being over gassed. It would not cycle the cases even with H1 and H2 buffers. I put a gas piston on it and it worked perfectly. I then tried a Syrac adjustable gas block on it and it worked perfectly also. LRRPF52 may be right about your carrier cycling too fast. You may want to try one of your adjustable gas blocks on it and see if that will correct your problem. It's obvious Hornady powder curve works in your rifle but not with your reloads. Gas pistons are more tolerant and self regulating compared to direct gas systems, but I do prefer direct gas systems for lighter recoil and accuracy.

[LRRPF52]

It could also be a carrier that is too large around the bolt tail. Take one of the carriers from your other Grendels, and try it in the problem gun with your hand loads.

[bobke]

Swapped out light buffer for an H2, left carbine spring in place and back to the range with a few more handloads with 123 AMax and 31.5 CFE and CCI 41's. They functioned and ejected without issue, though the lower pressure 8208/AMax load and 107 Sierra and 29.5 TAC would fire and eject, but still shortstroked and would not pick up next round. I'll try swapping out BCG's, but I did make sure washer gaps were all at 120d to each other to eliminate blowby, but I can only swap out to verify any additional clearance. Hadn't even considered that as a possibility-appreciate the heads up and assist. I'm still learning AR's every time I go out and this has baffled me quite a bit, but I've at least found functional loads to work with until a real solution is recognized.

[montana]

The washer gaps can be lined up and will function reliably. The washers turn all the time on the bolt when the rifle action cycles. It is a myth that the washer gaps lined up will cause malfunctions.

[LRRPF52]

The washer gaps can be lined up and will function reliably. The washers turn all the time on the bolt when the rifle action cycles. It is a myth that the washer gaps lined up will cause malfunctions.

The bolt gas rings are forced to fill the gap when the bolt is seated in the recess within the carrier, so lining up the gaps doesn't do anything, and they will shift as montana stated.

Sounds like you've got it mostly figured out. What does the brass look like on the loads with the 107gr? What is the velocity? 29.5gr of TAC under the 107gr SMK is a pretty decent load, and should be running the action reliably, in my opinion. I have run that load and much lower with TAC under the 100gr NBT, and never had a short-stroke. I have a 16" MLGS, with H2 buffer though.

I think most shooters had reliable functioning with that load through 20" guns though. Bwaites will know. TAC is one of my go-to powders in the Grendel, for 100-123gr bullet weights with long bearing surfaces. It will give you velocity, that's for sure. 120gr SMK has gone 2537 fps for me with TAC out of the 16" barrel. 100gr NBT has gone up to 2700fps for me, but I'm in higher pressure there, with primer and brass showing it.

[bobke]

107 Sierra/29.5 TAC avg'd about 2618 fps, 31.35 CFE/123 Amax about 2484 and 28.35 8208/123 Amax 2491. Factory Amax 2525 fps. Was unable to chrono 31.5 CFE, but figure very close to factory 123's. Small difference in velocity of handloads to short cycle as it is, but 31.5 CFE got me back to full function. I've got 40 more rounds of same loaded for further vetting the load/function.
Seems I've read that certain powder pressure curves behave differently, and some are more ideally suited for certain barrel lengths, regardless of powder burn rate and bullet weight, so wondering if CFE pressure curve may be better suited to this particular 20" barrel, but I really don't prefer to be limited in this manner. Gas hole is .81, and from reading back through various threads, may be on the small side, and surprised that loads so close to factory velocity do not cycle properly, even with lightest buffer and carbine spring. Barrel is .875 at block, and handguard very tight space, so only a limited number of options for an adjustable block present themselves.
LR-in reading through some of your guidance regarding bcg/gas tube/carrier key dimensions, do you have correct numbers for what they're supposed to be? I do have a couple of BCG's to try, key appears to be properly staked and I haven't torn into the remainder to check for leaks anywhere, but hadn't seen correct dimensions posted in looking through a lot of threads regarding port sizing, etc. Appreciate any guidance possible, as I'd prefer not to touch barrel/block, if able, and hope it's a less complicated issue elsewhere.