One in a million AR15 issue

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Find some reputable mil spec ammo and if it has the same problem you’ve prob got your answer.
 
@ny32182 - I know a lot of guys ignore the advantage and hate the idea of AGB’s, but personally, I almost never shoot an AR without one, and certainly don’t go suppressed without one. A couple clicks on a detent screw block and you can swap in and out of suppressed fire, swap from full pressure rounds to reduced loads, run heavy or light reciprocating masses at your will (aka swap to a different lower with a different buffer weight).

Well worth the confidence, in my book.
 
While that’s normally true I don’t believe there’s a setting on an agb that would result in popped primers from factory ammo. So something else is going on
 
Varminterror said:
@ny32182 - I know a lot of guys ignore the advantage and hate the idea of AGB’s, but personally, I almost never shoot an AR without one, and certainly don’t go suppressed without one. A couple clicks on a detent screw block and you can swap in and out of suppressed fire, swap from full pressure rounds to reduced loads, run heavy or light reciprocating masses at your will (aka swap to a different lower with a different buffer weight).

Well worth the confidence, in my book.
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I don't have a ton of experience with it, but my impression of 5.56 DI ARs suppressed does dovetail directly with this. Even with other ammo and the primers not popping out, brass comes out super dirty, often with more aggressive marks from the extractor/ejector, and my overall impression is that adding the can really increases the amount of gas running the system in a significant way. It runs, but certainly doesn't seem ideal. I haven't done back to back testing with one buffer weight vs. another, etc, to see what the impacts might be.

It isn't directly related to this, but I just got a Sig 516 upper delivered from one of the super sales; and if the piston and adjustable gas work as I think they might, I'll probably go to that rifle for just about any suppressed 5.56 shooting I want to do.

300blk on the other hand, my 12.5" upper built with AAC components runs great with my supersonic ammo, can or no can.

While that’s normally true I don’t believe there’s a setting on an agb that would result in popped primers from factory ammo. So something else is going on
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I'm almost sure that the primers are just not very tight in this batch of ammo, and the increase in back pressure of the can is somehow creating a situation where they are getting pushed out. The ones that are not pushed out are not cratered; they look fine. I can verify this with some factory fresh Federal AE soon enough.
 
taliv said:
While that’s normally true I don’t believe there’s a setting on an agb that would result in popped primers from factory ammo. So something else is going on
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Something else IS going on, as an AGB never causes popped primers, but rather - high port pressure, driving the bolt open while the case is still expanded and hanging onto the chamber which 1) gives the primer room to be blown out, and 2) has the force to blow it out once the room is created.

It MIGHT be that this one particular load is too hot, and would be on the ragged edge of any AR, or even blow primers. But if we assume it’s NOT an out of spec load with a non-compliant max pressure/port pressure, then limiting the gas exposure does solve the problem. Experimenting with different ammo, as already explicated in the OP’s observations, will change the way the rifle cycles, but there’s no denying that swapping from suppressed to non changes the operating bore pressure of the rifle, so avoiding that one brand of ammo might be THE solution to those blown primers, but adding an AGB remains to be A solution to the over-arching issue of variable pressure standards between firing conditions and ammo selection.

Like I said, I know a lot of guys really don’t care for AGB’s for some reason, but from a builder perspective, they’re well worth the reliability and operational control.
 
Doing a fresh search on what buffer people are using in midlength 16's, it appears all over the map. I might benefit from moving to an H or H2, given that this rifle ejects toward 2-3 oclock even without the can. Something to try at least.
 
my point is changing the gas is a minor tweak. like changing the buffer weight. the AR is running on the ragged edge of pressure with factory ammo and adding a suppressor puts it over the edge. sure, putting an AGB in there might pull it back so it's not popping primers, but it's not like it puts it back comfortably into the middle of the operating range. it's basically just masking a symptom.

that's dangerous because someday a little rain or dirt or something in the chamber that would cause a normal rifle to maybe pop primers, is going to cause this one to kaboom.
 
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taliv said:
my point is changing the gas is a minor tweak. like changing the buffer weight. the AR is running on the ragged edge of pressure with factory ammo and adding a suppressor puts it over the edge. sure, putting an AGB in there might pull it back so it's not popping primers, but it's like like it puts it back comfortably into the middle of the operating range. it's basically just masking a symptom.

that's dangerous because someday a little rain or dirt or something in the chamber that would cause a normal rifle to maybe pop primers, is going to cause this one to kaboom.
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There aren't really other pressure signs though: No cratering or pierced primers, visually screwed up case heads or splitting, etc.
 
@taliv’s cautionary statement is valid and fair.

The fact it only happens with one particular round is a good indicator that load is over-pressure. Doing so in a middy 16” is another indicator that the load is out of whack. Popping primers with suppressed AR’s is a pretty common symptom, as most AR’s are already over-gassed with standard, compliant pressure ammo (and I suppose to say they are technically under-massed if using a semi-auto carrier and/or carbine buffer), and adding the can out front only exacerbates the issue.

I generally don’t expect factory ammo, especially with a SAAMI compliance label, to be accidentally over MAP. A load running an odd powder with excessive port pressure can show blown primers while still falling under MAP.

I may also be guilty of assuming the OP isn’t very particular about the loads being fired, such the culprit load would only occasionally be in play, and giving up on this ONE round would be pretty easy and uneventful.
 
If you guys really think the load is overpressure I can pull them and either reduce the charge or just replace it with my own. Looking in my really old notes I don't seem to have any record of chronoing this batch either.
 
ny32182 said:
There aren't really other pressure signs though: No cratering or pierced primers, visually screwed up case heads or splitting, etc.
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You wouldn’t, necessarily.

A) It takes a LOT to rip a case head, especially for new rounds - so don’t expect that.

B) You mention other rounds dribbling out of the port - which, as I mentioned above, is a symptom of a weak extractor. So a weak extractor with an early unlock won’t leave significant scoring on the rim which one might expect.

C) Primer cratering can’t happen in a condition where primers are popping. Cratering only happens when the primer is held hard against the bolt face with an excessive pressure flowing the primer into the pin bore. Cratering isn’t a good indicator of pressure anyway. Equally, piercing only happens when the case is held against the bolt face and FP, holding the primer hard enough against the extended pin during the peak pressure. Blown primers happen when the bolt is withdrawing away from the round, leaving room for the primer to escape.
 
has he tried other ammo? did i miss that? i just read he had this ammo and handloads

edit: my post above should have said "not like" instead of "like like"
 
Other simple remedial repairs I suggest; Replace extractor assy, and replace ejector spring. (at least-while you'r in there, the ejector itself isn't a bad idea.) These are inexpensive, simple part swaps that while they may not have been the sole cause, could certainly have been contributory.
 
B) You mention other rounds dribbling out of the port - which, as I mentioned above, is a symptom of a weak extractor. So a weak extractor with an early unlock won’t leave significant scoring on the rim which one might expect.
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Sorry, did not mean to give the impression they are dribbling out; that is not the case. Strong ejection, but at 2-3 oclock which I understand means it might be overgassed for the buffer weight. Extractor tension feels fine to me compared to other guns, and I have had to replace extractor springs in the past... they seem to lose tension over time, even just sitting in the safe.

C) Primer cratering can’t happen in a condition where primers are popping. Cratering only happens when the primer is held hard against the bolt face with an excessive pressure flowing the primer into the pin bore. Cratering isn’t a good indicator of pressure anyway. Equally, piercing only happens when the case is held against the bolt face and FP, holding the primer hard enough against the extended pin during the peak pressure. Blown primers happen when the bolt is withdrawing away from the round, leaving room for the primer to escape.
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Ah ok. That makes sense.

I have shot handloads in this rifle with no issues, mostly 24gr Varget with 77gr SMK; I don't recall how much was suppressed though.

Will try different ammo and buffer weight and report back. Might be a couple weeks.
 
ny32182 said:
I'm almost sure that the primers are just not very tight in this batch of ammo, and the increase in back pressure of the can is somehow creating a situation where they are getting pushed out.
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This isn’t a thing. Primer tension in the pocket is never fighting the pressure of the round - primers are ALWAYS pushed out by the firing pressure, but the cartridge is then slammed backward to reseat onto it. We’re pressing primers into and out of place with a few pounds of pressure, and the firing pressure is 50-60kpsi... not even close...

What you’re seeing, in this case, is the primer is getting pushed too far out and the case is not moving with the primer, not secured to the bolt face.

We know his is happening at the BACK end of the combustion cycle, because your magazines aren’t getting blown out of your rifle and case-heads aren’t getting blown off. So what’s happening for you: the primer is pushed out of the case against the bolt face during primary ignition, the case is thrust backwards to reseat the primer as the bulk charge is ignited, the case expands to seal against the chamber, the primer cup expands to seal against the brass, then when the bullet passes the port, the gas impulse overpowers the action mass inertia, opening the bolt - BUT - the case is still under excessive pressure and holds onto the chamber wall, while the bolt moves rearward. Because the case is held momentarily in the chamber and the bolt is moving away, pressure pushes the primer back out of the case.
 
Varminterror said:
This isn’t a thing. Primer tension in the pocket is never fighting the pressure of the round - primers are ALWAYS pushed out by the firing pressure, but the cartridge is then slammed backward to reseat onto it. We’re pressing primers into and out of place with a few pounds of pressure, and the firing pressure is 50-60kpsi... not even close...

What you’re seeing, in this case, is the primer is getting pushed too far out and the case is not moving with the primer, not secured to the bolt face.

We know his is happening at the BACK end of the combustion cycle, because your magazines aren’t getting blown out of your rifle and case-heads aren’t getting blown off. So what’s happening for you: the primer is pushed out of the case against the bolt face during primary ignition, the case is thrust backwards to reseat the primer as the bulk charge is ignited, the case expands to seal against the chamber, the primer cup expands to seal against the brass, then when the bullet passes the port, the gas impulse overpowers the action mass inertia, opening the bolt - BUT - the case is still under excessive pressure and holds onto the chamber wall, while the bolt moves rearward. Because the case is held momentarily in the chamber and the bolt is moving away, pressure pushes the primer back out of the case.
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Wouldn't this result in a failed extraction?
 
Nature Boy said:
If I understand correctly this only happens with the Radway ammo. Everything else runs fine.

If true, I'd say the simplest answer is it's the ammo.
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unless... radway and his handloads are the only two ammo he's shot. we need to test another brand of factory ammo.
it is entirely possible that he got an overpressure lot of radway, but that is certainly not common. otoh, i can't tell you how many times i've seen ned's chamber tool fix out of spec factory chambers in carbine classes. and the symptom there was always the same: popping primers with factory ammo
 
ny32182 said:
Wouldn't this result in a failed extraction?
Click to expand...

The AR's extraction/ejection system is designed with redundancy in that if one of them fails, the other is designed to complete the action of getting the case out of the way. This is why proper extraction/ejection on an AR is so violent.
 
(Unfortunate) update:
I've shot some of this ammo through a couple other rifles unsuppressed with no issues.

Took the rifle in question out again today and tried out H1 and H2 buffer. With the H2 buffer unsuppressed, the ejection pattern changed to about 4 oclock (good, right?) Put the can on. First 15 or so rounds were looking good (remember 50% of primers were coming out with the regular carbine buffer).

Then with about 15 total rounds of the ammo left, a primer came out. Went to unload to make sure it was out of the action. Bolt was in battery with a live round in it, but wouldn't move.

Chose to fire the round in the chamber. Bolt made it back to the unlocked position, carrier about a half inch from fully closed. Pogoing, etc didn't result in any movement. Went home, mallet to the charging handle, nothing. Put a rod down into the bottom of the case and hammered it back just far enough to get the empty case out. That puts the carrier just far back enough to where I can't separate the upper and lower. :(

I have no leverage to get the carrier back forward. I'm 99% sure the primer is wedged between the carrier and the inside receiver wall. Probably galling a nice groove in the upper.

Extension is staked on, so would prefer not to take it off, but I can't think of any other way to get it apart right off hand.... any ideas? Its locked up tighter than a drum.
 
Would be interesting to take some measurements on the fired case necks. See if the chamber is tight at that juncture creating excessive case pressure before the bullet releases. OP could see if a new projectile can easily be pushed into the fired case, this would be normal as the case neck expanded. If not that means the chamber at the case neck is tight. Another thing to check would be for a thick neck on the fired case which would cause the same issue of preventing the bullet from leaving the case before pressure builds too much in the case.

Just something else to look at besides just simply over pressure rounds.
 
Didn’t see your last replay before I replied.

I would be checking some fired cases like I suggested for tightness.

The suggestions for a heavier H2 buffer are a good one when running the gun suppressed. This is why I have AGB on my rifles, as also was suggested. But you would be wise to figure out what is causing these primers to blow out because that is a problem with a cause of its own. I would be looking closely into the ammo and chamber dimensions of your rifle.
 
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