Can't get adj gas block set

[ported45]

I'm trying to get a buddy's adj gas block set correctly.

I likely followed the wrong internet instructions since none came with the upper. I started at 3 full turns out from bottom and it did not lock back on the catch; only caught on the mag. I kept turning it out until I was afraid I was going to lose the screw. Never did get proper lock back of the bolt.

The upper is a PSA. The adj screw on the front of the block looks like it has 3 or 4 detents on it and the set/lock screw is on the side. If I back out the set screw a full turn, I can barely feel the detent catches when I turn the adj screw.

Can the adj screw be turned out too far and cause a short stroke? That would not seem possible to me.

My extent of "working" on an AR consists of simple parts swapping, so if it comes down to removing gas blocks to check gas port diameter then my buddy just needs to move this thing on down the line to let someone else check it out for him.

I'm just wondering if it is at all possible to cause short stroking by having the adj screw too far out.

I watched a video last night of a guy only starting 1 full turn from bottomed out and he had the block set in 4 shots. Took a few more shots to confirm and that was it.

[VASCAR2]

[mtnlvr]

I'm guessing you can lock the slide back by simply using the charging handle and an empty mag / chamber?

If you have a good, functioning upper I'd try swapping it onto his. If the bolt doesn't lock back start looking at the recoil system. If it does lock back, it's likely an issue with the gas system.

Yes, the gas port could be undersized, but it's more likely that the block is out of alignment and would need to be loosened from the barrel and realigned. It's not to difficult.

With your good upper and his upper removed from their lowers, you can also compare how easily you can blow ait through the gas tube. I've used a section of vinyl tubing to extend the gas tube so I can blow into it. That may help you determine the block is out of alignment with the port.

There are plenty of tricks to help getting the port aligned. A piece of dried spaghetti is a good one. Toothpick works too. Just make sure you get it all back out.

If you end up taking the gas block off, measure the diameter of the port. That's best done with gage pins but you probably done have that. Next best is probably drill bits...find the biggest drill bit that goes through to the bore...by hand. You'd likely need a set of numbered drill though, not just in 1/16" increments. A caliper works OK too, but doesn't reach all the way to the bore to verify the hole goes as far as it should. At least visually make sure the hole looks clean to the bore.

You don't even need to take the muzzle device off or gas block completely off the barrel. Just loosen to slide it towards the muzzle. Now depending on your handguard design, that might get in the way.

There's really not a lot too it.

Of course if it's new, the manufacturer should fix it too under warranty, but then he's going to be without it for a bit.

[lazyengineer]

Fully remove both screws. Then insert your Allan wrench into the cavity to figure out which screw partially blocks the gas path, and which screw engages the other screw to hold it there.

Be aware such screws do tend to walk out btw. If they don't carbon lock.

Then track you screw position based on how many revolutions out from fully closed and bottomed out. Note that there will be a sweet spot where 1/8 turns matter. And everywhere else where it doesn't matter at all.

[ported45]

I'm guessing you can lock the slide back by simply using the charging handle and an empty mag / chamber?

If you have a good, functioning upper I'd try swapping it onto his. If the bolt doesn't lock back start looking at the recoil system. If it does lock back, it's likely an issue with the gas system.

Yes, the gas port could be undersized, but it's more likely that the block is out of alignment and would need to be loosened from the barrel and realigned. It's not to difficult.

With your good upper and his upper removed from their lowers, you can also compare how easily you can blow ait through the gas tube. I've used a section of vinyl tubing to extend the gas tube so I can blow into it. That may help you determine the block is out of alignment with the port.

There are plenty of tricks to help getting the port aligned. A piece of dried spaghetti is a good one. Toothpick works too. Just make sure you get it all back out.

If you end up taking the gas block off, measure the diameter of the port. That's best done with gage pins but you probably done have that. Next best is probably drill bits...find the biggest drill bit that goes through to the bore...by hand. You'd likely need a set of numbered drill though, not just in 1/16" increments. A caliper works OK too, but doesn't reach all the way to the bore to verify the hole goes as far as it should. At least visually make sure the hole looks clean to the bore.

You don't even need to take the muzzle device off or gas block completely off the barrel. Just loosen to slide it towards the muzzle. Now depending on your handguard design, that might get in the way.

There's really not a lot too it.

Of course if it's new, the manufacturer should fix it too under warranty, but then he's going to be without it for a bit.

The lower that we are using was just on his .223 upper and everything works flawlessly. Full, lock back of the .223 bolt.

I have since read several instructions from several manufacturers and most all of them say to start one full turn from completely closed and open a half a turn per shot till it locks back. I'm going to give it one more go like that and then I am giving it back to him to have someone else dig deeper into it or he can ship it back to PSA for them to look at.

Fully remove both screws. Then insert your Allan wrench into the cavity to figure out which screw partially blocks the gas path, and which screw engages the other screw to hold it there.

Be aware such screws do tend to walk out btw. If they don't carbon lock.

Then track you screw position based on how many revolutions out from fully closed and bottomed out. Note that there will be a sweet spot where 1/8 turns matter. And everywhere else where it doesn't matter at all.

I definitely have the screws figured out as one of them has the milled detents in it and the other would have completely closed off the gas since I had the adj screw unscrewed so far if I had them backwards. Believe me, the thought crossed my mind by the time I had shot the 8th shot and the bolt was not locking back completely yet.

[sundowner]

My PSA adj blocks adj on the side and the lock is the one in the front.

[mtnlvr]

Definitely sounds like it's an issue with the upper.

And I'm not sure that the PSA gas block variants will allow a completely closed off system. Not all gas blocks fully close.

[Klem]

45

In answer to your original question - In your case seeing the lower is fine, short stroking would occur because there's not enough gas pressure. This can be for a few reasons: the ammunition is not hot enough, not enough barrel length in front of the port (dwell time), the barrel's port is not wide enough, the port and block are misaligned, the gas block is not letting enough gas through, or there is a leak back at the carrier, maybe the key is loose.

I suppose if you unscrewed the AGB enough gas might leak around the threads, but it would have to be pretty loose. It's unlikely to be this.

If you know which screw does what on that block then my next check would be port misalignment. For that you need a bore scope, or take it off and do some careful measuring and marking (or the 'spaghetti method' on the other thread).

[ported45]

Definitely sounds like it's an issue with the upper.

And I'm not sure that the PSA gas block variants will allow a completely closed off system. Not all gas blocks fully close.

This one closes off enough to not eject. I started one full turn from bottomed out. Backed out until it finally locked open. Didn't on the next shot, so I opened it up another detent click. Didn't lock back.

Took it back home to grab more ammo and lubed the crap out of it thinking maybe it just wanted to run really wet. Back to the range and the first round locked back on the catch and the next didn't. Opened it up another click...no lock back. One more click open and still nothing. Threw in the towel at that point.

Packed it up and called my friend to come get his rifle and contact PSA about a return authorization. He picked it up last night and went straight to UPS to send back the upper.


Thanks to all who offered up advice. My thoughts are that something is misaligned somewhere or the gas port just isn't large enough to begin with. I still don't have the "AR tools" to properly tear into one of these, so I put it back on him to find someone else or ship it back. He called PSA and they said to send it back.

I do hope that they fix it and not just replace. The last trip I had set up a 100 yard target because I was hoping that it was going to be functioning and it put those 4 rounds into a half an inch with 28.0 of 8208 and 123 SST's.

And when I say no lock back, I mean on the bolt catch. Because it locks back on the mag every time that the adj screw is open far enough to get it to eject. In 24 rounds it only locked back on the catch twice.

[montana]

This one closes off enough to not eject. I started one full turn from bottomed out. Backed out until it finally locked open. Didn't on the next shot, so I opened it up another detent click. Didn't lock back.

Took it back home to grab more ammo and lubed the crap out of it thinking maybe it just wanted to run really wet. Back to the range and the first round locked back on the catch and the next didn't. Opened it up another click...no lock back. One more click open and still nothing. Threw in the towel at that point.

Packed it up and called my friend to come get his rifle and contact PSA about a return authorization. He picked it up last night and went straight to UPS to send back the upper.


Thanks to all who offered up advice. My thoughts are that something is misaligned somewhere or the gas port just isn't large enough to begin with. I still don't have the "AR tools" to properly tear into one of these, so I put it back on him to find someone else or ship it back. He called PSA and they said to send it back.

I do hope that they fix it and not just replace. The last trip I had set up a 100 yard target because I was hoping that it was going to be functioning and it put those 4 rounds into a half an inch with 28.0 of 8208 and 123 SST's.

And when I say no lock back, I mean on the bolt catch. Because it locks back on the mag every time that the adj screw is open far enough to get it to eject. In 24 rounds it only locked back on the catch twice.

Over gassing can cause many of the same symptoms as under gassing. Adj gas blocks will leak more gas than standard blocks and can cause short stroking if the system is not gas efficient..Gas tubes can be cracked or have a worn button that can not be seen unless removed or checked with a gas tube gauge. I have seen bolt carrier keys that were loose but would work in one rifle and not another..It is always best to send any problem child back to the manufacturer for warranty work....

[imaguy3]

You keep mentioning detents on the gas block. I have an adjustable psa with detents. The side screw does not get touched, it's only job is to hold the adjustment and detent mechanism in. The front screw is your adjustment screw and detents keep it from moving. It has a lot of clicks of adjustment. It sounds like you were on the verge of it working and probably needed to back it out a few more than where you had it.

Read the q/a:

https://palmettostatearmory.com/psa-custom-750-diameter-click-adjustable-gas-block-7811021.html

"Is the set screw on the side a lock screw or to adjust do I just click the front adjustment screw and leave it once set with no need to lock it with set screw on side?
Rich M.Nov 26, 2019

Best Answer: The set screw on the side holds the extent ball and spring in, no need to remove it unless you need to remove the adjustment screw completely."

[mtnlvr]

PSA has had several variants of gas blocks. The one I had from them did not have detents. I think it was from about 3 years ago.

[ported45]

You keep mentioning detents on the gas block. I have an adjustable psa with detents. The side screw does not get touched, it's only job is to hold the adjustment and detent mechanism in. The front screw is your adjustment screw and detents keep it from moving. It has a lot of clicks of adjustment. It sounds like you were on the verge of it working and probably needed to back it out a few more than where you had it.

Read the q/a:

https://palmettostatearmory.com/psa-custom-750-diameter-click-adjustable-gas-block-7811021.html

"Is the set screw on the side a lock screw or to adjust do I just click the front adjustment screw and leave it once set with no need to lock it with set screw on side?
Rich M.Nov 26, 2019

Best Answer: The set screw on the side holds the extent ball and spring in, no need to remove it unless you need to remove the adjustment screw completely."

I could not find the exact one that was on his upper on PSA's website. It only had three detents on the screw. The other I found on the site said that it had like 5 detents on its adjustment screw.

I loosened the set screw about a 1/4 turn just so the adjustment screw was easier to turn. I then would continue to open the gas block and still feel the detent notch and re-tighten the set screw on the side. I had it so far out at one point that I was afraid that it would come completely out. I thought I was just about there, but when I kept opening up the screw, it would still never lock back on the catch.

[ported45]

PSA has had several variants of gas blocks. The one I had from them did not have detents. I think it was from about 3 years ago.

It would be nice if they would send instructions since they seem to put whatever adjustable gas block on it that they have on hand so that a guy would know exactly how to adjust that particular block. But I guess since they use so many different ones that it is too hard for them to keep track of what directions go with what gas block.

[imaguy3]

I could not find the exact one that was on his upper on PSA's website. It only had three detents on the screw. The other I found on the site said that it had like 5 detents on its adjustment screw.

I loosened the set screw about a 1/4 turn just so the adjustment screw was easier to turn. I then would continue to open the gas block and still feel the detent notch and re-tighten the set screw on the side. I had it so far out at one point that I was afraid that it would come completely out. I thought I was just about there, but when I kept opening up the screw, it would still never lock back on the catch.

There was no reason to loosen the side screw that held the detent adjustment in. Tighten that back up and I bet your detent would work as it should. As far as thinking your there... you could have been way off, unless you took it all the way out you have no idea where the end was.