Completely stumped-yet another gas function question.

[Bobke]

Alright, this is starting to eat a hole in my brain. Have a new to me JP ultra light Supermatch 18" rifle gas barrel that has been installed in a known to function upper/lower setup. Seekins lower, rifle buffer tube, Tubb flat spring, Seekins bolt release, ambi, Geissele match/match trigger. Upper is Daniel Defense, Seekins adj gas block and JP barrel and Young NM carrier. All of which ran without issues with 24" Satern barrel and ASC mags.
Forward to JP barrel install which has matched JP bolt. With fully open gas block, three different springs, two bolts, tested in another rifle setup that functions 100% and a carbine setup that is 100% with a mid length gas barrel, the bolt and carrier will only retract to the point it may/may not pick up next round, but will never get to full retraction to bolt catch, only just as far as back end of mag-maybe. Gas aligned, new gas tube, no sign of leakage. Hell of it is, other than enormous frustration, is that as I expected, the barrel itself shows it is accurate. But does not function. I'm stumped. Have built nice selection of AR's in 223, 6.5 Grendel and 6.5 Creedmoor, ALL of which function 100% and all are quite accurate.
At wits end. Seems to be slowed down at bolt catch, which I've smoothed contour of, but to no avail. Feels like something is too long, but can't seem to see where. Fact it's doing same thing in two other lowers leads me to barrel and/or gas block, but they seem to be correct.
Calling on long time expertise here for an assist. Thanks.

[A5BLASTER]

Do you have the gas block tight against the shoulder on the barrel?

Also it maybe the gas block's port hole is not lineing up correctly, I spoke with JP once ashen I was setting mine up and they told me that some gas blocks may not work due to the port in the block would not line up because they were cut too adjust for the gap most barrels need between the shoulder and gas block.

JP barrels gas port or cut so the block has to be tight against the shoulder and will probably work best with their gas blocks.

I have the same barrel as you but I use the JP gas block.

I use the SCS but also have a standard rifle buffer and buffer spring and both will run properly.

[Bobke]

Have a JP clamp on, but have more hand guard clearance with Seekins and have an SLR set screw mount coming. Current Seekins GB tight against shoulder and correctly aligned. I'll try the JP today without hand guard, and see if that doesn't eliminate one more variable, but list of variables is getting pretty short.

[A5BLASTER]

If you have some calipers, messure from the shoulder to center of barrel's gas port, then messure gas block from back of block to center of gas port in the block.

That will tell you if the gas port in the block is set to much forward of the barrel's gas port even with it tight against the shoulder.

I had the same problem with two gas block's a Syrac click adjustable and a joebob's adjustable, even with the gas block tight against the shoulder they still wouldn't cover the barrel's gas port enough to get proper function.

I changed out to a JP gas block and it lined up perfectly.

I hope you get it figured out, it does seem like you are short on gas.

[A5BLASTER]

Also forgot look inside the block and make sure the hole in the gas tube is properly lined up with the hole in the gas block, had that issue before with the joebob's gas block.

[SG4247]

Funny, I had one doing that yesterday.

Turns out I had installed the wrong buffer.

There are several buffer lengths to pick from nowdays, and my short A2 length stock combined with the longer style buffer would prevent the carrier from locking on the bolt catch.

Installed the short buffer and it ran perfectly.

Might check that.

[A5BLASTER]

SG4247, good point I didn't think to mention that, but he does state it has a rifle buffer tube on the lower and a tubb's spring, I'm assuming he has a rifle length buffer in it, but you know how assuming things go.

[Sputnik]

Have you checked for gas port obstructions, and gas port diameter?

[Bobke]

Just installed a JP clamp on and heading to range. Was at range twice yesterday and the only thing to come of it was once fired factory brass. Need this to work-again because barrel shows lots of accuracy potential. Hoping next post is that GB was issue. Appreciate the assist, all.

[A5BLASTER]

Bobke, What buffer do you have in the lower right now?

[Bobke]

STD rifle AR15. Have std rifle, Tubb and JP tuned rifle springs standing by.

[A5BLASTER]

Ok just thought I would ask.

Like I had posted earlyer mine runs just fine with a standard rifle buffer and spring, so I don't think it's that but I could be wrong.

I think the problem is at the gas block.

[A5BLASTER]

Question, Is the spring up have in there right now a extra power spring?

[Bobke]

If either JP or Tubb would be considered so, I'd say yes. Just back from range and got it to work about 80-90%, and ran out of ammo. It's a start. May also try std strength spring, as I had to open gas quite a bit for function. Appreciate input guys-don't think I'm fully confident just yet.

[A5BLASTER]

Cool deal glad you are starting to make some headway on the problem.

How open do you think the block is open. On my rifle the gas block is close to have open and have proper function I can close it off a lil more but it runs perfect at that setting with the SCS and the standard rifle buffer and buffer spring.