View Full Version : Can't figure out adjustable gas block problems
Ok, these have me stumped. I'm not new to working on firearms but I just can't figure these out. Two separate builds similar issues. 1 is a 10.5" typical AR with superlative arms / PSA type adjustable gas block shooting wolf 55 grainers. Recoil's fine, and shells are ejecting at 4:30. With the gas block all the way closed I get short stroking issues as normal, but the second I open the gas block just enough (about 2 clicks) to make the bolt start locking open on the last round that's the end of the adjustability. NOTHING I do after that changes a single thing. It always ejects to the 4:30 position and that's it. It's like it's an on and off gas block, and I get zero adjustability out of it after the bolt begins locking to the rear. I know, odd.
Firearm 2 is a CAR15 build with JP's old school A frame adjustable gas block shooting the same ammo. Again, NO setting changes ANYthing. I've already opened the gas port up on this barrel once or twice by a thousandths each (can't remember the measurements) using the proper drill bits. On this weapon the bolt locks back EVERY time regardless of setting, and ejection is at 4:30 precisely. All the way open and all the way closed is the same thing for this. Zero change on any adjustment.
Anyone else have these issues?
Firearm 1: This already has an appropriately sized gas port, and doesn't need an adjustable gas block.
Firearm 2: Same as firearm 1, but also the gas block can't sufficiently restrict the gas flow because the pin doesn't go far forward enough to actually occlude the gas port.
Replace both gas blocks with non-adjustable ones.
Sounds like everything is fine.
Why mess with adjustable blocks?
Firearm 1: This already has an appropriately sized gas port, and doesn't need an adjustable gas block.
Firearm 2: Same as firearm 1, but also the gas block can't sufficiently restrict the gas flow because the pin doesn't go far forward enough to actually occlude the gas port.
Replace both gas blocks with non-adjustable ones.
Firearm 1's gas size is appropriate now? What port size is on there?
Sounds like everything is fine.
Why mess with adjustable blocks?
Because these firearms will be suppressed soon, and things need to be adjusted when they're suppressed. And even if they're not, I'm not really into letting the action batter itself to death (yes I shoot more than a magazine a year lol) for no real reason when I can have control over that action.
My point is that these gas blocks aren't really changing things drastically as I had thought, so I'm wondering if anyone else has any personal experience with these gas blocks not functioning as they're advertised I guess.
triggerjerk
11-07-21, 14:31
Fudd here. FWIW, my first AR ejected 4:30. 300 rounds in I sent pic of cam pin to one who knows. He said he had cam pins with 3000 rounds on them in much better shape. Enter adjustable gas block. If rifle ejected, it was to 4:30. Period. A couple or 4 thousand rounds later, I replaced extractor/spring. Ejection angle now varies with the heat of the load and/or block setting.
Note that I do happen to have my 3rd BRT gas tube coming.....
Shoot well, be safe.
vicious_cb
11-07-21, 16:45
Can't figure out adjustable gas block problems
I found the problem, you have an adjustable gas block. Throw that s**t away and get a regular gas block.
Important info to leave out of the original post...
The results of the same tests with a suppressor attached are likely to be quite different.
Adjustable gas blocks can't add Gas Drive beyond what the barrel port provides; they can only limit it.
Many designs can't shut gas all the way off either.
Because these firearms will be suppressed soon, and things need to be adjusted when they're suppressed. And even if they're not, I'm not really into letting the action batter itself to death (yes I shoot more than a magazine a year lol) for no real reason when I can have control over that action.
My point is that these gas blocks aren't really changing things drastically as I had thought, so I'm wondering if anyone else has any personal experience with these gas blocks not functioning as they're advertised I guess.
Important info to leave out of the original post...
The results of the same tests with a suppressor attached are likely to be quite different.
Adjustable gas blocks can't add Gas Drive beyond what the barrel port provides; they can only limit it.
Many designs can't shut gas all the way off either.
I get that, but it's good to know that many can't shut gas all the way off. THAT's good info lol, as I was ****ing going crazy lol.
I would contact JP. Since they cater to the competition market with low mass carriers etc. I would expect it to throttle quite far if not close all the way. Aero Precision sent out replacement screws for their blocks because the ones initially released did not allow enough range of adjustment.
I would contact JP. Since they cater to the competition market with low mass carriers etc. I would expect it to throttle quite far if not close all the way. Aero Precision sent out replacement screws for their blocks because the ones initially released did not allow enough range of adjustment.
Ok, called JP and they said it should shut all the way off. So I pulled the block and looked in and realized the set screw was hitting something that made me think it was maxed out. Dont know what it was but I overpowered it (it didn't take much, I just didn't want to be heavy handed is all) and now I can see it goes in a little further. Will try it all again in a few days to see what's up.
Ok, called JP and they said it should shut all the way off. So I pulled the block and looked in and realized the set screw was hitting something that made me think it was maxed out. Dont know what it was but I overpowered it (it didn't take much, I just didn't want to be heavy handed is all) and now I can see it goes in a little further. Will try it all again in a few days to see what's up.
Glad it was something simple.
RIFLESPEED
11-10-21, 10:35
As Clint mentioned (& it sounds like you know), things are going to change when you add a can. I’d add that with ejection at 4:30 you may be in a marginal performance situation unsuppressed. Ejection at 4:30 usually indicates minimal performance and you may experience failures in cold temperatures or with lower-powered ammo. That’s exactly the scenario that got us started years ago with a very accurate match barrel that cycled well until temperatures dropped. Once you get your cans, rerun your tests and keep in mind that there is no downside to a huge gas port that allows reliable function in all conditions with all ammo when you have a rugged and reliable method of controlling that gas delivered to your action.
Ejection angle doesn't have anything to do with how an AR is gassed. What affects ejection angle the most is the ejector assembly and the extractor assembly.
When I first started working with tuning ARs, I foolishly believed in the ejection angle pie chart. I say foolishly because prior experience with FALs had already taught me how to properly tune an adjustable gas block. A friend and I tried to tune one of his ARs using that ridiculous ejection angle pie chart. It does not work. What I found out through experimentation is that ejection angles tend to move forward as the extractor spring weakens. So, if you try tuning an AR that is ejecting forward because of a weak extractor spring, you end up with short stroking.
Set up the AR with the right gas drive (including the right ammo), the right buffer, the right action spring, the right extractor assembly and the right ejector assembly and let the ejection angle take care of itself. With or without suppressor.
RIFLESPEED
11-10-21, 11:49
So if I take an AR out to the range right now and fire while adjusting the gas from maximum to minimum there will be no change to the ejection?
So if I take an AR out to the range right now and fire while adjusting the gas from maximum to minimum there will be no change to the ejection?
The angle may or may not be a change. But it's not a reliable indicator of how an AR is gassed.
Once, I had an AR that was ejecting brass between 1 and 2 o'clock. The 10.5 inch barrel had a huge gas port, almost .085" and the only solution was an SLR adjustable gas block. No matter how much I cut off the gas, the angle stayed the same range until the AR started short stroking. Finally, the AR started having ejection issues. It'd leave the spent case in the action jamming the next round from the mag. I replaced the ejector spring. Still had problems. Swapped mags. Swapped BCGs. Tried different ammo. Checked for gas leaks. Nothing.
Finally, I replaced the extractor spring, tuned the gas block until the AR ejected but did not lock back, then opened the gas block one click until it locked back and ejected. No more ejection problems and the ejection angle came in around 3 to 3:30. In fact, the angle didn't change much from being overgassed (Not grossly because I didn't want to waste ammo, but enough you could feel the recoil was sharper than normal) to being just undergassed.
While tuning another AR, we did see the angle change as we adjusted the gas block. I didn't think anything about it at the time, but after a few hundred rounds the AR started having the same malfunction described above. Installing a new extractor spring fixed the problem.
My experience in troubleshooting ARs is that if there is a change in ejection angle, it's the extractor spring, not the the gas drive.
If the extractor spring is on the edge of failing, it will work fine at normal carrier speeds. But as the speeds increase, the spring is stressed and has less and less control of the extracted case. It cannot hold the case against the bolt face. Unless the case is held firmly against the bolt face to compress the ejector, ejection angle changes, usually forward, sometimes forward enough to bounce back into the action.
If an AR were so grossly overgassed it overwhelms even a good extractor spring, I suspect there will be a change in ejection angle.
RIFLESPEED
11-10-21, 20:15
Ejection angle doesn't have anything to do with how an AR is gassed
The angle may or may not be a change.
So anyway...
OP, good luck with your rifles. Sounds like you're on the right track to getting it sorted out.
So anyway...
OP, good luck with your rifles. Sounds like you're on the right track to getting it sorted out.
LOL! All you got out of my posts was "Ejection angle doesn't have anything to do with how an AR is gassed" and "The angle may or may not change"? You didn't pay attention to how the extractor spring affects angle or how an increase in BCG speed affects a weak or failing extractor spring.
That's ok. I'm just sumdumgoy on the internet and, as Abraham Lincoln, the 2nd President of the United States was so fond of saying, "You can't believe everything you read on the World Wide Web."
MistWolf, you made the case that forward ejection by itself is not indicative of an over-gassed gun, but what about the opposite that RIFLESPEED referenced? What combination of extractor and ejector effects will produce 4:30 ejection from a strongly gassed gun?
MistWolf, you made the case that forward ejection by itself is not indicative of an over-gassed gun, but what about the opposite that RIFLESPEED referenced? What combination of extractor and ejector effects will produce 4:30 ejection from a strongly gassed gun?
That's an interesting question I hadn't considered. I've never encountered 4:30 ejection.
Hmmm...
The angle may or may not be a change. But it's not a reliable indicator of how an AR is gassed.
Once, I had an AR that was ejecting brass between 1 and 2 o'clock. The 10.5 inch barrel had a huge gas port, almost .085" and the only solution was an SLR adjustable gas block. No matter how much I cut off the gas, the angle stayed the same range until the AR started short stroking. Finally, the AR started having ejection issues. It'd leave the spent case in the action jamming the next round from the mag. I replaced the ejector spring. Still had problems. Swapped mags. Swapped BCGs. Tried different ammo. Checked for gas leaks. Nothing.
Finally, I replaced the extractor spring, tuned the gas block until the AR ejected but did not lock back, then opened the gas block one click until it locked back and ejected. No more ejection problems and the ejection angle came in around 3 to 3:30. In fact, the angle didn't change much from being overgassed (Not grossly because I didn't want to waste ammo, but enough you could feel the recoil was sharper than normal) to being just undergassed.
While tuning another AR, we did see the angle change as we adjusted the gas block. I didn't think anything about it at the time, but after a few hundred rounds the AR started having the same malfunction described above. Installing a new extractor spring fixed the problem.
My experience in troubleshooting ARs is that if there is a change in ejection angle, it's the extractor spring, not the the gas drive.
If the extractor spring is on the edge of failing, it will work fine at normal carrier speeds. But as the speeds increase, the spring is stressed and has less and less control of the extracted case. It cannot hold the case against the bolt face. Unless the case is held firmly against the bolt face to compress the ejector, ejection angle changes, usually forward, sometimes forward enough to bounce back into the action.
If an AR were so grossly overgassed it overwhelms even a good extractor spring, I suspect there will be a change in ejection angle.
This is good intel; I will check this stuff as well. Thanks!
As Clint mentioned (& it sounds like you know), things are going to change when you add a can. I’d add that with ejection at 4:30 you may be in a marginal performance situation unsuppressed. Ejection at 4:30 usually indicates minimal performance and you may experience failures in cold temperatures or with lower-powered ammo. That’s exactly the scenario that got us started years ago with a very accurate match barrel that cycled well until temperatures dropped. Once you get your cans, rerun your tests and keep in mind that there is no downside to a huge gas port that allows reliable function in all conditions with all ammo when you have a rugged and reliable method of controlling that gas delivered to your action.
This is exactly why I'm concerned. I wanted to tune this with low powered ammo (55 grain wolf) so that it's barely in the acceptable zone, so that when I use good quality 62 grainers, I'm hoping that the slight additional punch will put it where it needs to be (more torwards the 3 o clock) and be a tad more reliable. I think I have a hand on this now and will try a few experiments mentioned here. I just found it odd that changing the settings on these blocks had very little effect on the ejection pattern and I wasn't satisfied with that.
Also remembered that the polished recoil spring I have in one of the guns with the JP A frame gas block is a +5% stiffer spring...
The BCG that's in that gun is a plain jane "nickle boron" coated bcg from AIM, and I have to say it's definitely on the cheaper side of the house and has a questionable extractor spring in it. I will take this really nice Failzero bolt I have that has a nice hard ejector spring and an extractor with both the rubber tophat and o ring in it, and change that out to see if that has any effect on the ejection angle, along with this standard issue recoil spring that I have. I'll change one thing at a time to see what happens.
Install a Colt extractor spring before starting. No O ring.
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