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C4IGrant
09-14-08, 15:41
http://www.ar15.com/forums/topic.html?b=3&f=118&t=393112&page=1

Anyone want to bet that the DPMS had a tight chamber and there was a pressure spike?? ;)



C4

MX5
09-14-08, 16:21
The half dozen DPMS bbls that I've run a finish reamer into were all marked '5.56', but there sure is a lot of metal coming out of them.

jmart
09-14-08, 17:00
I'm not buying it Grant. That's an ammo problem, either bullet setback or something seriously amiss, with either the Hornady cartridge or a squib from the preceding Silver Bear.

A brand new cartridge case can contain a decent pressure spike, but when something goes kaboom, pressures are well beyond what you would see from NATO ammo fired in a SAAMI chamber.

Robb Jensen
09-14-08, 17:07
Probably somehow fired slightly out of battery.

jmart
09-14-08, 17:14
How can an AR fire OOB? I'm trying to picture how the firing pin can protrude far enough beyond the bolt face to strike the primer, but the bolt not rotating and seating behind the locking lugs.

Robb Jensen
09-14-08, 17:16
How can an AR fire OOB? I'm trying to picture how the firing pin can protrude far enough beyond the bolt face to strike the primer, but the bolt not rotating and seating behind the locking lugs.

Broken firing pin or too much firing pin protrusion which is why there is a MINimum and a MAXimum on the firing pin protrusion gauge.

Iraqgunz
09-14-08, 17:24
We had the same thing happen here just before I arrived in October 2007 with a Bushmaster M4gery. Unfortunately, no one documented the ammo or conditions. It blew the barrel extension apart and messed up both the lower and upper receiver. My guess is that there was possibly a squib round, although I would venture to say that it would have also caused a malfunction and it should have been noticed. Hard to say. Personally I would not have let anyone dick with it until I had taken photos and documented everything first.

Since he was firing different types of ammo and unless they can recover the casing (headstamp) Hornady could easily say that the damage isn't their fault (my opinion only). It could also be a combination of tight chamber, ammo, etc...Voodoo?

jmart
09-14-08, 17:31
If you read the whole thread, Hornady is being very stand up about it. They've inspected the other unfired cases from the OP's lot and they determined the brass was good (no annealing issues). They also fired the remaining cartridges w/o issue. Next up is an inspection of the gun. Apparently the barrel didn't burst so I doubt there was a Silver Bear squib round stuck in the bore, but something is amiss. And I still think it's something much more than a tight chamber. Could be a combination of things actually.

Robb Jensen
09-14-08, 17:40
I don't think it was a squib, as most that I've seen are much more catastrophic. It sounds like he really only perm. damaged the mag and the gun is 'locked up' which means the casing is expanded too much. How does this happen, firing slightly out of batter or too long of a round (as seen with 'Canned Heat'). I say slightly out of battery since the casing can't expand bigger than it's own chamber. I'm sure there's other damage like a cracked bolt, damaged extractor, damaged CAM pin and/or firing pin. Possibly the carrier is cracked or carrier key and charging handle also may be damaged.

Factors that I believe contributed to this problem:

DPMS = 'too tight', because we (DPMS) think customers care more about accuracy vs. reliability, 5.56mm NATO is the way.
Steel cases = leaves a lot of stuff in the chamber (on DI guns) which might have been enough to keep the bolt from completely locking but just enough for the firing pin to light off the primer.

Iraqgunz
09-14-08, 17:43
Robb,

I am just pissing in the wind on this. Would definitely like to see some pics and find out what damage was sustained and the end cause. Hopefully we will get some more poop when everyone is done doing the fingerbang.


I don't think it was a squib, as most that I've seen are much more catastrophic. It sounds like he really only perm. damaged the mag and the gun is 'locked up' which means the casing is expanded too much. How does this happen, firing slightly out of batter or too long of a round (as seen with 'Canned Heat'). I say slightly out of battery since the casing can't expand bigger than it's own chamber. I'm sure there's other damage like a cracked bolt, damaged extractor, damaged CAM pin and/or firing pin. Possibly the carrier is cracked or carrier key and charging handle also may be damaged.

Factors that I believe contributed to this problem:

DPMS = 'too tight', because we (DPMS) think customers care more about accuracy vs. reliability, 5.56mm NATO is the way.
Steel cases = leaves a lot of stuff in the chamber (on DI guns) which might have been enough to keep the bolt from completely locking but just enough for the firing pin to light off the primer.

jmart
09-14-08, 17:48
Just posted this on TOS on a similar thread (http://www.ar15.com/forums/topic.html?b=3&f=118&t=395043) with the same ammo (Hornady purched through Cabella's), where the OP had several primers pop in his RRA. The following pertains more to that type of situation than the more severe incident that's being discussed here, but I still think it's somewhat relevant to the general issue of pressure spikes in general:


Could be a couple of things, bad ammo, tight chamber that's not really a 5.56. Another thing it could be is a carbon ring that's formed just in front of the throat/leade area.

Give your barrel a good cleaning. Use a good carbon cutting cleaner and/or some IOSSO bore paste or JB. Short stroke through the throat area with a tight patch and make sure it is absolutely spotless and cleaned down to the bare metal/chrome. Alternate with a bronze brush and scrub the area. Don't assume the area is clean unless you've been pretty aggressive previously -- some solvents just end up cleaning around the ring, but the ring remains. Get that area clean.

Some powders are worse than others in this regard. Even if you are one the guys who doesn't clean that often and subscribes to the "just keep lubing it" theory, it pays to ensure your locking lug area,chamber, and the first couple of inches of the bore are kept clean. JMHO.

C4IGrant
09-14-08, 18:05
I'm not buying it Grant. That's an ammo problem, either bullet setback or something seriously amiss, with either the Hornady cartridge or a squib from the preceding Silver Bear.

A brand new cartridge case can contain a decent pressure spike, but when something goes kaboom, pressures are well beyond what you would see from NATO ammo fired in a SAAMI chamber.

Happens all the time. As the rep at Hornady said, they shot the rest of the ammo and there was zero issues. .223 chambers with 5.56 Pressure equals bad things. We see it all the time.


C4

C4IGrant
09-14-08, 18:07
I don't think it was a squib, as most that I've seen are much more catastrophic. It sounds like he really only perm. damaged the mag and the gun is 'locked up' which means the casing is expanded too much. How does this happen, firing slightly out of batter or too long of a round (as seen with 'Canned Heat'). I say slightly out of battery since the casing can't expand bigger than it's own chamber. I'm sure there's other damage like a cracked bolt, damaged extractor, damaged CAM pin and/or firing pin. Possibly the carrier is cracked or carrier key and charging handle also may be damaged.

Factors that I believe contributed to this problem:

DPMS = 'too tight', because we (DPMS) think customers care more about accuracy vs. reliability, 5.56mm NATO is the way.
Steel cases = leaves a lot of stuff in the chamber (on DI guns) which might have been enough to keep the bolt from completely locking but just enough for the firing pin to light off the primer.

Agree. NO squib, tight chamber and extra residue in the chamber from steel ammo.


C4

C4IGrant
09-14-08, 18:09
Just posted this on TOS on a similar thread (http://www.ar15.com/forums/topic.html?b=3&f=118&t=395043) with the same ammo (Hornady purched through Cabella's), where the OP had several primers pop in his RRA. The following pertains more to that type of situation than the more severe incident that's being discussed here, but I still think it's somewhat relevant to the general issue of pressure spikes in general:


Popping primers is generally always because of tight chambers.

I have reamed just about every tier 3 AR barrel and I am here to tell you that none of the are true 556 NATO chambers.


C4

Robb Jensen
09-14-08, 18:17
Robb,

I am just pissing in the wind on this. Would definitely like to see some pics and find out what damage was sustained and the end cause. Hopefully we will get some more poop when everyone is done doing the fingerbang.

I don't think you are dude,
I missed the part about Hornady getting it apart and finding no damage.
I'd like to see the parts and the rifle as well. I'm sure there more damage then Hornady is telling him. ARs don't just vent gas through bottom of the chamber for no reason, I know he said the case ruptured but that shouldn't really do anything except get stuck in the chamber. The bolt shouldn't have unlocked before the pressures within the barrel had significantly dropped. I think it's probably a combination of things. Too tight and a very dirty chamber, a bad case, too big of a gas port, too light of a buffer (bolt moving too early)...........all for the perfect storm, if you will.




Papabri:
**UPDATE**

Both the AR and the remaining 298 rounds were sent to Hornady in Nebraska. Todd at Hornady has been very helpful in letting me know what they are doing.

He was able to get the spent case out, and it suffered a case separation at the rear of the case (sorry, no pics). What they don't know as yet is what caused the separation.

Hornady did a lab test on the remainder of what I sent back and found no annealing problems. Todd shot the remainder of the box I opened and all fired without a problem.

He said that DPMS will get the gun from him and do their own inspection. Todd said that from what he could tell, there was no damage to the rifle. They were also going to do some sort of chamber cast to see if there are any deficiencies with the chamber.

I'll provide another update when I know what the next step is. I'll ask Todd at Hornady about the suspicion about soft points. I'm no expert, but it would seem like a soft point, as opposed to a FMJ, would take up the pressure if it misfed, and not push the bullet further into the case.

It's pretty damn weird to me. I've only seen guns this has happened to and it was all 'Canned Heat' ammo which uses military cases that are often from M249s which lengthens them and makes them weaker.

jmart
09-14-08, 19:02
Happens all the time. As the rep at Hornady said, they shot the rest of the ammo and there was zero issues. .223 chambers with 5.56 Pressure equals bad things. We see it all the time.


C4

What happened here does not happen all the time. This was a minor kaboom. Minor kabooms happen for reasons other than just a tight chamber.

I'll grant you that primers can pop, caseheads after multiple reloadings can separate (although virgin brass shouldn't), etc., but you don't have minor explosions going on in those instances. There's something else at work here. (The 2nd thread BTW had some interesting happenings, same ammo, same lot).

It could have been a bad round (light charge weight) that resulted in SEE. The rest of the ammo could have been fine. It could have been a minor bore obstruction. It could have several things that led to "the perfect storm" as Robb mentioned, but a SAAMI chamber by itself doesn't cause a kaboom.

RD62
09-14-08, 21:33
http://www.ar15.com/forums/topic.html?b=3&f=118&t=393112&page=1

Anyone want to bet that the DPMS had a tight chamber and there was a pressure spike?? ;)



C4

It couldn't possibly have been an out of spec chamber because it was a DPMS chamber and they have 5.56 Nato chambers, and supply parts to the .mil, and are just as good as the Colts and LMT's and Noveske's you sell, and are alot cheaper. :D

Seriously though, maybe he can pick up the tab for his friends Dr bills for his finger, with the money he saved buying the DPMS.

-RD62

Spooky130
09-14-08, 23:40
I've been following this on TOS and I think it sounds like a tight chamber. The guns it happened in are somewhat known for their non-5.56 chambers (RRA and DPMS). I think the gun at Hornady was going to have a cast of the chamber taken - that will be quite telling.

I saw this ammo on the shelves at Cabela's in DFW the other day. 50 rounds to the box and looks just like the practice ammo (box only). I know Hornady makes you sign a waiver to get the real 5.56 TAP and I wonder what this stuff really is. On TOS someone mentioned it was an overrun from a contract with an LE agency in Kentucky...

Spooky

vigilant2
09-15-08, 06:30
Geez, tight chambers, large ports, unstaked castlenuts you guys are driving
me crazy!:eek:
Okay,Okay, I give up and give in. I'll take my RRA entry tactical as backup for
the CDM4LE this week to carbine class. After that its history:( . I'll
forget about the fact that I shot several sub-moa groups with it the first time
out to the range with it. Also that I love that RRA 2-stage trigger :) .
After reading this and other threads I going to lose sleep worrying about
switching between the decent quantity of AE 55gr and XM193 I have on
hand.
Have to do something, Grant put me on your list for a BCM middy! E-mail
coming! I'm starting to feel better already:D .

MX5
09-17-08, 09:24
...I have reamed just about every tier 3 AR barrel and I am here to tell you that none of the are true 556 NATO chambers.


C4

Amen.

skyugo
09-17-08, 13:25
DPMS = 'too tight', because we (DPMS) think customers care more about accuracy vs. reliability, 5.56mm NATO is the way.
Steel cases = leaves a lot of stuff in the chamber (on DI guns) which might have been enough to keep the bolt from completely locking but just enough for the firing pin to light off the primer.

oh yeah.. somebody buying a 600 dollar DPMS rifle really wants it to put all 10 bullets inside of a quarter. :rolleyes:

i think most people buying low end AR's would be much happier with a gun that went bang every time. :p I know that was my focus when i built up my low end AR.

Robb Jensen
09-17-08, 15:29
oh yeah.. somebody buying a 600 dollar DPMS rifle really wants it to put all 10 bullets inside of a quarter. :rolleyes:

i think most people buying low end AR's would be much happier with a gun that went bang every time. :p I know that was my focus when i built up my low end AR.

I know, it's funny that's the excuse that DPMS always uses about their chambers being out of spec. I think it's funny that they had to make a device to keep the popped primers from getting down in the lower......treating the symptom instead of the problem. But I guess they think people want 'em ack'er-it. ;)

LOKNLOD
09-17-08, 15:49
oh yeah.. somebody buying a 600 dollar DPMS rifle really wants it to put all 10 bullets inside of a quarter. :rolleyes:



I know, it's funny that's the excuse that DPMS always uses about their chambers being out of spec.

Unfortunately when the majority of rifles only see 50-100 rounds per year from a bench at a range with "slow fire" requirements, shot by guys whose point of comparison is a 10x scoped hunting rifle....then group size/accuracy is going to be the only measure of "quality" that the rifle is held to.

Robb Jensen
09-17-08, 15:59
Unfortunately when the majority of rifles only see 50-100 rounds per year from a bench at a range with "slow fire" requirements, shot by guys whose point of comparison is a 10x scoped hunting rifle....then group size/accuracy is going to be the only measure of "quality" that the rifle is held to.


I agree.

Bimmer
09-17-08, 17:51
I know Hornady makes you sign a waiver to get the real 5.56 TAP...


Huh? I just ordered and received 200rnds of Hornady 5.56 TAP. No signatures involved.

Ben

C4IGrant
09-17-08, 18:16
Huh? I just ordered and received 200rnds of Hornady 5.56 TAP. No signatures involved.

Ben

Not direct from Hornady you didin't.



C4

Bimmer
09-17-08, 18:33
Not direct from Hornady you didin't.
C4

Yeah, I got a 200-round case from Ammo-Man for somewhere... I didn't even need to fax in my driver's license.

Ben