OP
OP
Charlie98
Member
Let's go have a look...
Do AR gas rings wear?
- Thread starter Charlie98
- Start date
Let's go have a look...
OP
OP
Charlie98
Member
Here's what we have...
The buffers. The old one is a hair shorter... whether that is because the bumper is hammered, I don't really know. It's not destroyed, and is still quite rigid.
Bolt retraction with the old buffer is about even with the rear port, the new buffer not quite so much.
Old buffer...
New buffer...
It does not appear the gas key is hitting the lower... I don't see any witness marks or swapped paint.
Of my 3 carbine builds... I currently have, the newest one on the left, a PSA kit gun... the bolt goes further back than any of the others, including my high mileage one. The DPMS rebuild (R) has about as much bolt travel as my problem child (center.)
The buffers. The old one is a hair shorter... whether that is because the bumper is hammered, I don't really know. It's not destroyed, and is still quite rigid.
Bolt retraction with the old buffer is about even with the rear port, the new buffer not quite so much.
Old buffer...
New buffer...
It does not appear the gas key is hitting the lower... I don't see any witness marks or swapped paint.
Of my 3 carbine builds... I currently have, the newest one on the left, a PSA kit gun... the bolt goes further back than any of the others, including my high mileage one. The DPMS rebuild (R) has about as much bolt travel as my problem child (center.)
lysanderxiii
Member
The tolerances make that distance variance much wider than 0.020".
The nominal dimension is 0.131", but there is over 0.070" tolerance, most of it from how deep the receiver extension threads into the lower. Remember the thread is a 16 pitch, there is a full 1/16 inch variation right there.
BTW it is normal for cases to hit the rear opening of the ejection port
https://www.youtube.com/watch?v=ZblsdxwZ7l0
If you get little kisses like this on your brass, the case is hitting the rear of the ejection port during ejection. It is NOT necessarily a bad thing
If it is more than a little kiss (below) you might have a problem.
Varminterror
Member
- Joined
- Jul 17, 2016
- Messages
- 14,893
Dings this high on the case are irrefutably from the shell deflector, NOT port rim contact.
Worn buffer bumpers don’t typically create - independently - the issue we’re seeing here. Bumpers should be ~7/16” behind the buffer body, and the compressibility is actually quite low, even in high bolt velocity scenarios. We should see something greater than 1/8” of bolt lug ahead of the port rim when locked, so even being flush, the bumper has to compress greater than 1/4 of its length, which takes a lot more force than we should be seeing in a properly built rifle.
So what happens - someone puts together a rifle which is ALMOST too much travel, flush or near flush bolt face to the port rim when pulled fully to the rear, so with a little wear and tear, it’ll start giving up enough compression that the side of the case hits that port rim while the extractor still has ahold of the case, and the case gets smacked in the ass instead of the middle of the body - you can see in those videos the case bouncing off of the deflector and bouncing OUT of the rifle, rather than back into it.
Chasing the wrong rabbits won’t get you fed. It’s easy to confirm bolt travel. But there’s no gas tube influence here. We see clearly that the old buffer was near flush with the port when pulled back, which is out of spec - and under compression, the lower end of the case WOULD bounce off of the port rim, rather than from the deflector as designed.
So again…
Dings this high on the case are irrefutably from the shell deflector, NOT port rim contact.
Worn buffer bumpers don’t typically create - independently - the issue we’re seeing here. Bumpers should be ~7/16” behind the buffer body, and the compressibility is actually quite low, even in high bolt velocity scenarios. We should see something greater than 1/8” of bolt lug ahead of the port rim when locked, so even being flush, the bumper has to compress greater than 1/4 of its length, which takes a lot more force than we should be seeing in a properly built rifle.
So what happens - someone puts together a rifle which is ALMOST too much travel, flush or near flush bolt face to the port rim when pulled fully to the rear, so with a little wear and tear, it’ll start giving up enough compression that the side of the case hits that port rim while the extractor still has ahold of the case, and the case gets smacked in the ass instead of the middle of the body - you can see in those videos the case bouncing off of the deflector and bouncing OUT of the rifle, rather than back into it.
Chasing the wrong rabbits won’t get you fed. It’s easy to confirm bolt travel. But there’s no gas tube influence here. We see clearly that the old buffer was near flush with the port when pulled back, which is out of spec - and under compression, the lower end of the case WOULD bounce off of the port rim, rather than from the deflector as designed.
So again…
Of course, this issue - as stated above - is exacerbated by excessive carrier speed, but independently, high carrier speed doesn’t do this. Since the new buffer bumper will stop the backwards case jam, problem solved, I’d move onto solving the overgassing issue also.
(By the by, I’m not going to pretend anything about that video with extreme bolt bounce is representative of a properly tuned AR. Just gross).
OP
OP
Charlie98
Member
When I was looking at my rifles yesterday, I did not a bit of an oddity...
If you look at the shell deflector on my problem child, the brass buffing is closer to the receiver...
Both of the other carbines show brass buffing at the outer edge of the deflector. Oddly enough, the newest one (the PSA build) ...the bolt retracts so far, you can't see it looking at a 90^ angle into the ejection port. This rifle only has 200 or so rounds through it since I built it... so I still have some work to do on it.
OP
OP
Charlie98
Member
Friend of mine had a 5.56mm AK... that rifle would actually bend the brass. The charging handle would catch the brass on the way back into battery and literally crease it.
lysanderxiii
Member
You're going to have to explain why those small dings in the cases also appear in M16A1s and other models without case deflectors . . .
OP
OP
Charlie98
Member
Given the track record with this rifle, I didn't want to go and change a bunch of things at once... and not know what actually fixed the problem, that's why I just replaced the spring with a standard weight, and went up one on the buffer (H1.) I probably won't get to it this week, to test drive it, again... hopefully next week.
Varminterror
Member
- Joined
- Jul 17, 2016
- Messages
- 14,893
You’re going to have to explain how ~1.76” cartridge cases have dents halfway up their length after an ejection cycle which puts their TAIL nearly flush with the port… (Acknowledging that those are 5.56 cases, not 308)… for that position to be dented by the port rim, those cases would have had to have had their tails riding against the inside wall, the off side, of the upper receiver - and doing that after they were pushed out of the action by the ejector on that side, the off side, of the upper receiver…
Ain’t my first rodeo with AR’s and witness dents. Not surprised at all to see the OP confirm the problem I stated - the bolt is withdrawing too far and the port is smacking the case in the tail, flipping them back into the action. This is the only failure mode which cases that result.
Skylerbone
Member
@Charlie98 you’re going to have to be ok with there being no boogeyman. Much ink has been spilled over the years with good intentions and little more than guesses.
There are clear remedies documented based on your issues and a clear course of remedial action if you can discern engineering facts being given you from guesses being offered.
There are clear remedies documented based on your issues and a clear course of remedial action if you can discern engineering facts being given you from guesses being offered.
OP
OP
Charlie98
Member
That's why I'm working through each item one by one. The comments posted are helping me understand what to look for, and why... not only with this particular weapon, but others as well... because I'm sure this won't be my last AR failure.
Sgt_Mike1
Member
hmmmm did you measure the free length of the buffer recoil spring ? (for mil spec spring free length it is 11-1/4" to 10-1/16" measured removed from rifle and buffer detached, I will replace the spring at 10-1/8" with a new one even though the manual says replace at 10-1/16")
What about the coil count on the spring ? (again Mil spec carbine is 37-39 coils) .
10 years and 3K the spring could have taken a set and be too short.
I
What about the coil count on the spring ? (again Mil spec carbine is 37-39 coils) .
10 years and 3K the spring could have taken a set and be too short.
I
Last edited:
OP
OP
Charlie98
Member
I didn't measure it, but I laid it on the desk next to the NIB one... and they were, basically, the same length. I would have to dig it out of the trash to measure it...
Sgt_Mike1
Member
Charlie the reason I mentioned the measuring the recoil spring is that it is a way to trouble shoot the system and the First place I check. A shortened spring with a set can increase the velocity of the carrier as well as too light buffer, or a light carrier. A kink in the spring can have the opposite effect, but depending on the situation could also do the same.
The other area I would look at is the gastube (look for kinks, bends, dents, rubs, interference with handguards, burnt area, small holes, excessive wear on one side of the tube where it fits inside the gas key of the carrier, alignment issue. A misalignment could have been done on installation not really likely but is possible. And been laying dormant until now, or now has created a gas leakage by wear of one side versus the other). Check the FSB / gas block for leaks, it could have loosened check snugness I don't know if your FSB / gas block is taper pinned, set screws,or clamped, but that doesn't matter what does matter is that it is snug.
Carrier when is the last time you actually cleaned the bolt path inside the carrier? Is there carbon on the bolt around the gas rings are the gas rings bent? misaligned? if all looks good move on. Check the gas key for obstructions, by using a small wire to go inside the key, of course the bolt and firing pin should be removed. Using a q-tip to clean the key sometime deposits part of the swab creating a short stroke.
If we was closer I'd probably meet with you as I highly suspect the issue is so simple it isn't funny.
But this is like diagnosing that my dodge 5.7 hemi is running rough what the problem?? 6 months of internet conversation turns out to be the alternator.
The other area I would look at is the gastube (look for kinks, bends, dents, rubs, interference with handguards, burnt area, small holes, excessive wear on one side of the tube where it fits inside the gas key of the carrier, alignment issue. A misalignment could have been done on installation not really likely but is possible. And been laying dormant until now, or now has created a gas leakage by wear of one side versus the other). Check the FSB / gas block for leaks, it could have loosened check snugness I don't know if your FSB / gas block is taper pinned, set screws,or clamped, but that doesn't matter what does matter is that it is snug.
Carrier when is the last time you actually cleaned the bolt path inside the carrier? Is there carbon on the bolt around the gas rings are the gas rings bent? misaligned? if all looks good move on. Check the gas key for obstructions, by using a small wire to go inside the key, of course the bolt and firing pin should be removed. Using a q-tip to clean the key sometime deposits part of the swab creating a short stroke.
If we was closer I'd probably meet with you as I highly suspect the issue is so simple it isn't funny.
But this is like diagnosing that my dodge 5.7 hemi is running rough what the problem?? 6 months of internet conversation turns out to be the alternator.
OP
OP
Charlie98
Member
Much of what you suggest I have already looked at. I swapped the gas block and tube early on in it's life, and I've already pulled it in regards to my current failures. There are no abnormalities that I can see. As I mentioned earlier, I can see the gas port is properly aligned, and there is not an inordinate amount of carbon blowby on the carrier key, the gas tube, or the receiver vents. Torque on the gas block screws was correct. I ran a pipe cleaner down both the gas tube and the key to make sure there was not an obstruction.
I recently... after the last episode of jams... soaked and cleaned the bolt and carrier. I use a cleaning tool for the carrier to clean the bolt... there was some gunk, but nothing out of the ordinary.
Now... here's the real kicker...
I pulled the old buffer spring out of the trash... and laid it next to the Expo Arms standard spring, and the Sprinco standard (white) spring. The tired, old spring is LONGER than either of the other springs... and, in fact, the Sprinco spring is the shortest by about 3/4"
BushMaster-15
member
Charlie98 ; Chit happens and as You yourself mentioned you've done nearly all .
An over-gassed gun pushes the limits of the platform by attempting to extract cartridge cases prematurely.
Because the brass isn’t ready, your AR could suffer feeding and ejection issues, carbon buildup, excessive recoil, and other issues.
One way to diagnose an over-gassed AR is to assess your ammo for gouges at the base of the cases.
Another method is the one-round test. Try running the gun with a full magazine and then switch to a mag with a single round.
If the gun behaves the same with both magazines, it’s probably over-gassing.
An under-gassed gun tends to slow down with a full magazine.
It may be okay at first, but then it fails to feed the next round. Or maybe it ejects slower and slower as you attempt to finish off the magazine.
If the gas tube and block are the correct size and properly aligned, that’s good news. But if you can’t open up that gas block, then it’s probably time to upgrade to an adjustable model.
With an adjustable gas block, you can tweak as needed for different loads. It’s amazing how one little upgrade can improve your AR’s accuracy and reliability.
Quick tip, builders: Dimple your barrels when installing the gas block. This small step could save you some frustration down the road.
Double Feed
As the term implies, a double feed is when two rounds try to enter the chamber at the same time.
This can be tied to a Failure to Extract, where a live round gets stuck behind the previously fired round or its case.
A major cause of double feed is an overly-full magazine.
As I mentioned before, you might have a 30-round mag, but that doesn’t mean you need to load it with 30 (or more ) cartridges.
Under-loading by a round or two can lessen the risk of tension-related failures.
Stove piping :
You can start by swapping out the magazine and trying a different brand of ammunition. If you’re still having trouble, check to see if the AR is under-gassing or over-gassing.
During this assessment, be on the lookout for fouling and verify if any brass shards are obstructing the bolt face.
All else fails , Talk to Gunny over in Sniper's Hide .
An over-gassed gun pushes the limits of the platform by attempting to extract cartridge cases prematurely.
Because the brass isn’t ready, your AR could suffer feeding and ejection issues, carbon buildup, excessive recoil, and other issues.
One way to diagnose an over-gassed AR is to assess your ammo for gouges at the base of the cases.
Another method is the one-round test. Try running the gun with a full magazine and then switch to a mag with a single round.
If the gun behaves the same with both magazines, it’s probably over-gassing.
An under-gassed gun tends to slow down with a full magazine.
It may be okay at first, but then it fails to feed the next round. Or maybe it ejects slower and slower as you attempt to finish off the magazine.
If the gas tube and block are the correct size and properly aligned, that’s good news. But if you can’t open up that gas block, then it’s probably time to upgrade to an adjustable model.
With an adjustable gas block, you can tweak as needed for different loads. It’s amazing how one little upgrade can improve your AR’s accuracy and reliability.
Quick tip, builders: Dimple your barrels when installing the gas block. This small step could save you some frustration down the road.
Double Feed
As the term implies, a double feed is when two rounds try to enter the chamber at the same time.
This can be tied to a Failure to Extract, where a live round gets stuck behind the previously fired round or its case.
A major cause of double feed is an overly-full magazine.
As I mentioned before, you might have a 30-round mag, but that doesn’t mean you need to load it with 30 (or more ) cartridges.
Under-loading by a round or two can lessen the risk of tension-related failures.
Stove piping :
You can start by swapping out the magazine and trying a different brand of ammunition. If you’re still having trouble, check to see if the AR is under-gassing or over-gassing.
During this assessment, be on the lookout for fouling and verify if any brass shards are obstructing the bolt face.
All else fails , Talk to Gunny over in Sniper's Hide .
OP
OP
Charlie98
Member
Using the blank adapter on my M16A1, in full auto, as the magazine empties the cyclic rate speeds up... it usually gets going really good... then that 30rd mag empties.
I don't normally use 30's... I'm a 20rd mag guy. When I am load testing, as I was when the problems showed up, I'm likely to only have 5 or 10 rounds in the mag. My normal mags are a combination of USGI 20 gen-u-wine Colt mags, or 20rd PMags.
The gas block I have on it now was an expensive PRI rail that I really like... unfortunately, it's non-adjustable. It's worked fine up to now, and I would be very reluctant to replace it at this point. I'm with you on adjustable blocks, however... my builds going forward will have one, if possible.
I have the last batch of brass in a box, when I get time this weekend I'm going to pull it out and have a look.
Skylerbone
Member
These tidbits are useful to mention from the outset because conditions (ammo) changed thereby altering the background story (ran flawlessly for xx rounds). Something to keep in mind for all posters, share details.
If the gas block is easily removed I would pull it off and measure the port size to start with.
Once you know all of the variables it's easier to determine what's going on.
For a 16" carbine gas a 0.0625" gas port is sufficient to run a blue spring and H buffer.
I have a PSA 16" car gas barrel with a gas port size of about 0.068", that's just about Mk18 territory.
It was locking back with an A5H4 (8oz) buffer and still flinging brass.
For measuring the gas port, gauge pins are the most precise.
The set I have is .250 - .500" and I didn't feel like buying more.
A good pick can be used like a taper gauge, just mark the pick at the journal and measure with calipers.
Or a master drill set with numbered, lettered, and fractional bits can get you close as well.
They are not gauge pins so if a .068" drill bit fits the hole then the hole size is just a bit bigger than that.
A .068" pin would be a press fit in a .068" hole, so gauge pins are under sized.
I replaced the PSA barrel with a 16" mid length and it was flinging brass with an A5H4 buffer.
Start poking around, measure the port and it's .081".
Seems .076" is the sweet spot for middy's
I calmed that one down with a BRT gas drive sized to use an A5H2 buffer, green spring and brass ammo.
It worked as advertised, won't lock back with an A5H4 buffer, won't cycle steel ammo, runs like a champ with an A5H2 buffer and 5.56 ammo.
You can get them sized for whatever you are using, suppressed etc.
The next two barrels I did a lot more research before buying them.
Not many companies list their port size and you have to poke around and see what others have measured.
Gas port sized for optimal use in the description is vague at best.
In Wilson Combats 18" barrel case, that's about a .099" gas port according to my gauge pick, TDP for a Mk12 is .0995"
Sheesh, why can't they just list the port size?
Faxon didn't publish the port size but they do explain how they come up with their port size.
Open it up until it locks back with a dry phosphate BCG and steel ammo, then a bit more to make sure.
For a 16" middy that came out to .081"
I don't run my guns that way so don't need all that gas.
My gas system is tight so don't need more gas due to blow-by.
SOLGW publishes all of their barrel data.
I found this useful when I was poking around.
https://soldiersystems.net/2020/08/10/fighting-gun-101-gas-ports/
Once you know all of the variables it's easier to determine what's going on.
For a 16" carbine gas a 0.0625" gas port is sufficient to run a blue spring and H buffer.
I have a PSA 16" car gas barrel with a gas port size of about 0.068", that's just about Mk18 territory.
It was locking back with an A5H4 (8oz) buffer and still flinging brass.
For measuring the gas port, gauge pins are the most precise.
The set I have is .250 - .500" and I didn't feel like buying more.
A good pick can be used like a taper gauge, just mark the pick at the journal and measure with calipers.
Or a master drill set with numbered, lettered, and fractional bits can get you close as well.
They are not gauge pins so if a .068" drill bit fits the hole then the hole size is just a bit bigger than that.
A .068" pin would be a press fit in a .068" hole, so gauge pins are under sized.
I replaced the PSA barrel with a 16" mid length and it was flinging brass with an A5H4 buffer.
Start poking around, measure the port and it's .081".
Seems .076" is the sweet spot for middy's
I calmed that one down with a BRT gas drive sized to use an A5H2 buffer, green spring and brass ammo.
It worked as advertised, won't lock back with an A5H4 buffer, won't cycle steel ammo, runs like a champ with an A5H2 buffer and 5.56 ammo.
You can get them sized for whatever you are using, suppressed etc.
The next two barrels I did a lot more research before buying them.
Not many companies list their port size and you have to poke around and see what others have measured.
Gas port sized for optimal use in the description is vague at best.
In Wilson Combats 18" barrel case, that's about a .099" gas port according to my gauge pick, TDP for a Mk12 is .0995"
Sheesh, why can't they just list the port size?
Faxon didn't publish the port size but they do explain how they come up with their port size.
Open it up until it locks back with a dry phosphate BCG and steel ammo, then a bit more to make sure.
For a 16" middy that came out to .081"
I don't run my guns that way so don't need all that gas.
My gas system is tight so don't need more gas due to blow-by.
SOLGW publishes all of their barrel data.
I found this useful when I was poking around.
https://soldiersystems.net/2020/08/10/fighting-gun-101-gas-ports/
OP
OP
Charlie98
Member
Keeping it simple stupid... I just said Lake City. My malfunctions occurred, largely, with it, anyway, and certainly as of late, in both my DEC and FEB range sessions with it... where I was only shooting LC. I also used LC as my control ammunition when I started trying to troubleshoot the problem... thinking if it doesn't cycle with 2 different types of LC, there is a problem with the gun, not the ammunition.
BushMaster-15
member
Just ran all the possibilities I could think of for malfunction scenarios .
It sure ACTS like it's a gas problem ,from what You've described .
I just ran MY latest build ,of which I had #2 failure to feed due to My Dumbazz . Long of it short popped a couple of primers from IFFY cases and grabbed UNsized replacements ; Didn't make battery ,Duh !. Interesting failed to lock back on empty mag Twice ,however rectified itself after running #20 rounds down bore . Not unlike yourself , I also run short mags when breaking in or load development .
I'll run the scenario by Gunny over in the Hide and see what if anything we've missed .
DustyGmt
Member
I still have the original gas rings on all of my AR's except for one. Not exactly sure what happened or what caused it, but the rifle still functioned fine but upon disassembly I noticed a gas ring bent and sheared right off to a sharp point. Strange occurrence and I wish I knew what caused it, only thing I can think is I was running the rifle really hard that week and it might have been quite dry for a period of time but still, the way they broke was so strange.
If I spent an hour digging through my phone I could find the pic, if I find it I'll post it. I'm sure I'm one of a few people on here that can actually show you gas ring trouble.....
If I spent an hour digging through my phone I could find the pic, if I find it I'll post it. I'm sure I'm one of a few people on here that can actually show you gas ring trouble.....
DustyGmt
Member
Found it. Not sure what the cause of this is but at this point I'd guess the rifle had between 3K-5K rounds through it and like I said, I was running it hard and dry. I think I was actually sick of shooting that week and had like 3 or 4 magazines left and was losing daylight so I pumped through them pretty quick and didn't notice a problem but when I got home this is what I found.
I have no idea how long they could have been this way because the rifle continued to run buy anyways, here is some worn/broken gas rings:
I have no idea how long they could have been this way because the rifle continued to run buy anyways, here is some worn/broken gas rings:
