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Posted: 1/13/2006 9:51:32 AM EDT
I have/had a sweet AR until Wednesday, took 100 rounds to the range to test, on the second shot the gun ka-boomed. The 23 remaining rounds in the (brand new) mag headed south and bulged the hell out of the bottom of it, and scattering rounds all over. Couldn't get it open, after an hour of pounding once I got it home, I got the bolt and carrier out of the receiver, what a mess. The bolt was apparently driven back hard enough into the carrier to peel away the bottom end of the bolt, bulge the carrier, and consequently the receiver. The fired shell has a section about 3/16ths of an inch that is badly blown out, the extractor still wears a large chunk of brass where the shell blew out, and the fired case shows severe signs of an over-pressure load, but shouldn't have. The load was one I have used for a year, 26.0 grains of Varget under a 55 grain Hornady V-Max bullet, no chance of an overload since I weigh every charge and have shot this load with different bullets for a couple of years without incident.

The fact that the base of the shell is blown out makes me think the gun wasn't in battery when it fired, is that a realistic assumption? The first shot was dead-on, right where it should have been, the second (and last) was several inches away and had a "tail" on the target like the slug was coming apart as it impacted, a sure sign of high pressure. Upon firing, the gun went into convulsions, smoke poured out everywhere, and I was unhurt but knew instantly something had gone wrong. The load is a grain and a half under maximum, and the brass was probably fired a half-dozen times or more when I loaded it.

So I'm out 500 bucks, and I can't figure out why. The bolt and carrier are trashed, the receiver is slightly bowed, and probably not salvageable.

I'm not sure if this is germain, but that same morning, I had installed a cheapo (Cheaper-Than-Dirt ) 4-position collapsible stock, mounted a weaver rail on the underside of the forestock, and attached a vertical grip. The spring provided with the buttstock was stouter than the A-2 spring it replaced.

Anybody had this happen? I expected old brass to seperate above the head if it blew, and the worst problem I'd have would be a rimless case stuck in the chamber. I can deal with that, I just never expected an upper with fewer than 1500 rounds thru it to totally munch itself to death. The lower unit and the bolt are from an Oly Match Target I bought several years ago, I added the Del-Ton upper less than a year ago. Prior to Wednesday, it had performed so well I was ready to buy another, and maybe several more. Any ideas on why it went ka-boom?

Papajohn
AKA confused about the kablooie in St. Louie
Link Posted: 1/13/2006 10:01:51 AM EDT
Pics!!!
Link Posted: 1/13/2006 10:06:15 AM EDT
Link Posted: 1/13/2006 10:10:39 AM EDT

Originally Posted By papajohn:
The bolt was apparently driven back hard enough into the carrier to peel away the bottom end of the bolt, bulge the carrier, and consequently the receiver.



I'd wait for the opinions of wiser, more experienced voices than mine before coming to a conclusion... but the above excerpt sounds like what I would expect from a out of battery condition. Lot of presure in those things, so the damage you are seeing is normal pressure uncontained.

As for a root cause... dunno... The fact that you put a new stock/recoil combo on there would be one of the first things I suspected. It'd also depend on how much of a "clean gun freak" you are. If you are like me, and scrub every bit of carbon out after each use, then it isn't an issue.
Link Posted: 1/13/2006 10:12:26 AM EDT
Glad to see you weren't hurt.
Link Posted: 1/13/2006 10:13:49 AM EDT
Tag.
Link Posted: 1/13/2006 10:27:42 AM EDT
Sorry to hear about your gun, glad to hear you still have all fingers.
Link Posted: 1/13/2006 10:31:02 AM EDT
Link Posted: 1/13/2006 10:43:25 AM EDT

Originally Posted By RevDeadCorpse:

Originally Posted By papajohn:
The bolt was apparently driven back hard enough into the carrier to peel away the bottom end of the bolt, bulge the carrier, and consequently the receiver.



I'd wait for the opinions of wiser, more experienced voices than mine before coming to a conclusion... but the above excerpt sounds like what I would expect from a out of battery condition. Lot of presure in those things, so the damage you are seeing is normal pressure uncontained.

As for a root cause... dunno... The fact that you put a new stock/recoil combo on there would be one of the first things I suspected. It'd also depend on how much of a "clean gun freak" you are. If you are like me, and scrub every bit of carbon out after each use, then it isn't an issue.



Glad you were not hurt
Sorry to hear about the loss of your rifle

From the description you give I will also speculate it was an out-of-battery condition. There are other possible causes, but not enough information to go by yet. If you have pics, please post!

Link Posted: 1/13/2006 10:47:47 AM EDT
[Last Edit: 1/13/2006 10:49:29 AM EDT by Triple_D]
Glad you are OK. Sounds a lot like a high pressure blow to me.



The fired shell has a section about 3/16ths of an inch that is badly blown out, the extractor still wears a large chunk of brass where the shell blew out, and the fired case shows severe signs of an over-pressure load, but shouldn't have.


This is typical of a high pressure blow in the AR. The case blows out under the extractor, and the extractor is usually bent outwards like a banana. There is also usually a large amount of brass that flows back into the ejector hole, in a high pressure blow.


The fact that the base of the shell is blown out makes me think the gun wasn't in battery when it fired, is that a realistic assumption?

It is hard to fire an AR out of battery, because the firing pin doesn't really protrude through the face of the bolt, unless the bolt is fully locked. High pressure will cause the case to blow out under the extractor, even if it is in battery.



Hard to speculate on the cause, Is it possible you loaded the wrong bullet...say a 77grain?
Link Posted: 1/13/2006 10:59:35 AM EDT
Link Posted: 1/13/2006 11:03:55 AM EDT
Tag

Sean
Link Posted: 1/13/2006 11:10:39 AM EDT
I wish I could post pics, but I can't. My main question is.....can this gun fire when it's not in battery? I never knew it could. After the first sdhot fired, I retrieved the case, and inspected it, the primer was a tad flattened, but nothing outwardly disturbing, since I use Federal (Soft) primers for everything. This load has proven accurate with numerous other slugs before, I'm just astounded it could do this kind of damage. As to powder problems, I always keep my powders well seperated, it was a batch of Varget that I have already tested for consistency, and it seemed a little slower than my last batch, given my tests in the 35 Remington I also shoot it in. In fact, I got a 3-shot group with the 35 that gave me .382" Gross group at fifty yards. So the powder's not suspect. My data shows a max charge of 27.5 grains, which would be compressed. Mine was'nt, the powder levels were all to the base of the neck in both 35 and 223. I just can't figure out why the gun fired out of battery, I clean it meticulously, every time I shoot it. I switched to Varget because I had good results with IMR-4895, but the action was gummy after 100 rounds. I remembered that Varget had been a lot cleaner-burning, so I went back to a load I'd shot plenty of before, with a different upper. Is there something I might have done wrong that I'm not thinking of? This whole thing has me perplexed. Anyone with any ideas is welcome to ask, I'm totally clueless as to what went wrong. I've been reloading for 25+ years, this whole thing is blowing my mind!

Thanks for all replies, and yes, why I still have all my fingers, toes, and eyeballs intact is a blessing and a mystery, for as much harm as I've placed them in the way of!

Papajohn
Link Posted: 1/13/2006 12:26:22 PM EDT
Sometime posted a picture a while back where a piece of the previous rounds primer stuck to the bolt face. On the next shot it fired the round out of battery because of the small raised material on the bolt face.
Link Posted: 1/14/2006 6:06:09 AM EDT

Originally Posted By papajohn:
I wish I could post pics, but I can't.

Where are you in MO? I've got a friend who can help with the pictures if needed in the St. Louis area and I'll be glad to post.
Link Posted: 1/14/2006 6:09:36 PM EDT
I had picked up and inspected the first round fired, it was totally intact, the neck, the primer, all of it. I keep the gun meticulously clean, usually only fire 50-100 rounds at a time, shooting groups. The fact that the gun clearly fired out of battery is what confuzzes me, I didn't know that was possible. I spent about an hour on the phone with a tech from Del-Ton (who sold me the upper) and he was as perplexed as I was. My faith in the AR system is badly shaken at this point, I've been handloading for 25+ years, and have never had a problem before this. I want to blame weak brass, but deep down I think the rifle did something wrong, firing while not totally locked in battery. I don't have a digital camera, or I'd love to post some pics. (I'm in St. Louis, South City.) I won't know if the upper is salvageable until I put a new bolt and carrier in it, and see if the rails are warped. As much as I love(d) this gun and system, I'm a little leery about buying another.

Papajohn
Link Posted: 1/14/2006 6:26:10 PM EDT
Had the bolt fired out of battery, you would have the bolt and buffer imbedded in your shoulder.

You had brass failure. Cause by either over pressure, or fatigued/annealed/scratched/damaged brass.

With chamber pressures around 50,000 psi, I don't feel the need to reload cases more than once.

Link Posted: 1/14/2006 6:33:29 PM EDT
Not according to the Tech at Del-Ton. The shell was clearly not all the way into the chamber, the action was NOT locked, and the bolt was ruptured to the point that it jammed it's way back into the carrier, and had to be pounded out. Took about an hour, and a lot of hammering. I have the evidence in front of me.

PJ
Link Posted: 1/14/2006 6:39:47 PM EDT
[Last Edit: 1/14/2006 6:51:57 PM EDT by j3_]

Had the bolt fired out of battery, you would have the bolt and buffer imbedded in your shoulder.


The carrier is not in a sealed tube. The pressure would expand throughout the upper and lower as the carrier moved backward.

Have you considered that the bullet may not have been crimped well and was pushed into the case as it was loaded in the chamber? This would have increased the pressure. V max does not have a cannelure does it?
Link Posted: 1/14/2006 6:56:30 PM EDT
That's always a possibility, but the fact remains the case was not fully seated in the chamber. The back 3/16" is blown out to a larger diameter, clearly not contained in the chamber. As to the pressure driving the bolt/carrier into my shoulder, most of the pressure was vented down into the mag well, blowing the remaining 23 rounds out the bottom of the mag, bulging the mag, removing the floorplate. Anyone who thinks the bolt would become a rear-moving projectile doesn't understand the situation, or physics. The mass of the bolt and carrier would preclude building enough inertia to blast the works backwards, especially since the carrier was split like a banana.

My one remaining question is how the damn thing managed to fire out of battery.

PJ
Link Posted: 1/14/2006 7:09:16 PM EDT
Without pics, it is hard to acess the damage.

As I understand youe description, the case blew out at the extractor cut in the bolt face. (?)

OOB firing would most certainly have resulted in total case head seperation.

OOB firing (bolt not locked) would have resulted in chamber pressure impinging directly on the bolt as in a blowback action. Nothing would have restricted the rearward travel of the bolt/carrier assy untill the carrier impacted the end of the kower extension tube. This also happens should youleave the cam pin out of the carrier assy and fire the weapon. In this case the bolt goes home, but the lugs do not lock resulting in a blowback action.

With the cam pin installed (and an inspec length firing pin) it is impossible for the hammer do make the pin hit the primer, the pin will not protrude enough untill the bolt rotates into battery. Take a carrier assy out of an upper and play with it to see what I mean. This is designed into the system.

Having much experience with highly stressed metal failures, I am guessing the brass was at fault.

The area of failure is unsupported during firing in the Ar. This works the brass quite hard with full power loads. Subsequent firings could have caused that spot to further weaken. The extractor also exerts force in this area during extraction. The surface of the failed area was loaded in tension turing the height of the chamber pressure. Any slight scratch or stretch from earlier firings could have caused a stress riser, which caused the brass to fail.

Link Posted: 1/14/2006 7:22:26 PM EDT
[Last Edit: 1/14/2006 7:28:04 PM EDT by ar-wrench]
Did it look like this? This was not an out of battery firing.

Description of this kaboom :

When the bolt was finally removed from the barrel extension, it was found that the rear of the cartridge case had been crumpled and looked like a belted magnum. The extractor had been blown loose, with its front section bent back into the barrel extension. This is what stopped the rotation of the bolt. When the extractor blew, it took a piece of the base of the case with it, [or more likely, vice versa;



Go to the Fulton Armory site and read what they have to say about reloading for gas guns.
Link Posted: 1/14/2006 8:58:46 PM EDT
I still don't buy the "out of battery" as was pointed out the firing pin isn't long enough to extend through the bolt face until closed. Now if you've got some other kind of indentation on the case head and primer you might be right. Now I've had a KB of my own with some very old ammo that ripped the case head off the rest of the cartridge and also blew out the bottome of the magazine, so I've sort of been in your shoes. I am thinking that you are actually looking at an early opening of the bolt while still under pressure with a suspect reloaded case.

I am sorry that you now doubt the 'system.' I'd have hoped that all your previous experience would have shown you that all in all it's a pretty good 'system.'
Link Posted: 1/14/2006 9:07:28 PM EDT

Originally Posted By j3_:

Had the bolt fired out of battery, you would have the bolt and buffer imbedded in your shoulder.


The carrier is not in a sealed tube. The pressure would expand throughout the upper and lower as the carrier moved backward.

Have you considered that the bullet may not have been crimped well and was pushed into the case as it was loaded in the chamber? This would have increased the pressure. V max does not have a cannelure does it?



+1
Link Posted: 1/14/2006 9:26:25 PM EDT
Were you able to recover the primer of the cartridge that blew up? If so, did it have an ordinary dimple?
Link Posted: 1/14/2006 9:49:38 PM EDT
[Last Edit: 1/14/2006 10:05:58 PM EDT by Kaliburz]




What if the load was under charged? Not enough powder to fill the case. I've heard of a 357 Mag undercharged and blew the cylinder in half & top strap off. Primer was exposed to "void" and ignited the top of the powder......and it burned accordingly, not the usual back to front. Could have it happend in this case instance? The pressure spiked and the case failed......

If the carrier is not all the way forward, it will go click, but not fire. Look at the carrier bounce the AR pistols have....if the carrier is just a hair from being 100% forward, it will go click, but won't go bang....don't see how the AR fired out of battery. Other then something else setting off the primer.....

Link Posted: 1/14/2006 10:18:10 PM EDT
was the brass trimmed to proper length?
Link Posted: 1/14/2006 10:43:37 PM EDT
taggage.

Glad you were not hurt.
Link Posted: 1/15/2006 4:40:20 AM EDT
Barrel obstruction........50,000 psi at the chamber if the barrel is clear the pressure at the muzzle has dropped to around 10,000 psi.

In your first post you stated you found signs of fragmentation on the target. Is it possible that a fragment was left in the barrel?

Did you find any signs of bullet impact on the target from the round that blew?


Not an expert, I have been reloading and shooting for a while.........Jim
Link Posted: 1/15/2006 4:43:07 AM EDT
Tag. Waiting for pics
Link Posted: 1/15/2006 4:48:07 AM EDT

Originally Posted By Norge1956:

Originally Posted By j3_:

Had the bolt fired out of battery, you would have the bolt and buffer imbedded in your shoulder.


The carrier is not in a sealed tube. The pressure would expand throughout the upper and lower as the carrier moved backward.

Have you considered that the bullet may not have been crimped well and was pushed into the case as it was loaded in the chamber? This would have increased the pressure. V max does not have a cannelure does it?



+1



My first thought. Take one of your handloaded rounds and push the tip of the bulet against a table straight on with a bit of force. If it goes in you've found the problem. It should take considerable force to push it in.
Link Posted: 1/15/2006 5:01:24 AM EDT
There is a portion of the rear of the case that is not supported by the chamber. I had a barrel once with a short throat in it. With some 55grain FMJ the bullet hit the rifling. It would bulge the end of the case near the rim when I shot the that ammo.
Link Posted: 1/15/2006 8:25:45 AM EDT
The more I look into this, the more confused I get. I have no pics to post, so I'll give you everything I know.

1. The Load is not suspect. The charges were weighed, and I have used this load for a few years. The base of the bullet rests on the powder column, and even shoving on it won't force it deeper. The powder was fresh, and had already been tested for consistency. The bullet had no cannelure, but neck tension was still good. This is why I always strive for 95+% load density, and chose Varget.

2. The first round fired was normal. I examined the brass,, the primer indent was normal, the headstamp was not smudged, the case was clean and totally unremarkable. The shot went exactly where it should have.

3. The 2nd round kaboomed. The bullet struck the target low and 4 inches left of the first, with a small curly tail under the hole, but the hole was perfectly round.

4. The fired brass that kaboomed has the look of a belted shell, with a third of the circumference missing. The extractor still holds a piece of the rim. The gas was vented straight down into the mag well, blowing out the remaining rounds and the spring thru the floorplate. There was a lot of smoke, and the bottom of the fired/damaged shell is blackened. The primer indent is normal. The "Belt" extends just above the web, and is fairly concentric.

5. The bolt was jammed back into the carrier hard enough to peel the lower section off, I broke it loose trying to get the mess out of the receiver. The bolt/carrier was jammed solid with the bolt head still close to the chamber, but not locked. The receiver is slightly bowed.

I still have both shells, and I am pretty sure bad brass is at least partially to blame. I tumble my brass until it gleams, to make it easy to find cracks, split, or other problems. Could an over-long case keep the bolt from locking up properly, yet still allow the rifle to fire? The deeper I get into this, the less sure I am about ANYTHING. I love my AR's, but the idea that this could happen when I try to stay well ahead of potential problems just gives me the willies. I had a factory 45ACP load blow the head in a 1911 years ago, and haven't shot one since. I like my fingers, eyeballs and other appendages where they are, and plan on keeping them intact.

So what could this have been caused by, given what I've listed here? Early unlocking? Bad brass combined with something else?

Papajohn
Link Posted: 1/15/2006 10:17:58 AM EDT
[Last Edit: 1/15/2006 10:18:31 AM EDT by ar-wrench]
" Could an over-long case keep the bolt from locking up properly, yet still allow the rifle to fire?"

An overlong cas can dramatically raise chamber pressures, especially in a .223 chamber as opposed to a 5.56 chamber.

BTW, glad you are OK. I, too, am a long time reloader.
Link Posted: 1/15/2006 10:37:39 AM EDT
Link Posted: 1/15/2006 10:38:28 AM EDT
Because the bullet touches the powder does not mean it will not go in further. I used to shoot a compressed load of win 748. Powder was up in the bullet area when I seated.
Link Posted: 1/15/2006 10:45:08 AM EDT

Originally Posted By papajohn:
Could an over-long case keep the bolt from locking up properly, yet still allow the rifle to fire?
Papajohn



More specifically, an overlong case neck. Not only could a KB result, but this is my best guess as to what happened. If the bullet is forcibly crimped on chambering b/c of excessive case length astronomical pressures can result. This is merely one type of high pressure overload. A primary failure of the case head (eg. improper annealing) is possible, but rare. Had you been using a bolt gun you might have noticed the increased resistance to closure on the round that KBd.......but, of course............

ARs do not fire OOB, but case heads do rupture when unsupported. The reason the OOB myth persists is b/c folks forget that the AR is not a bolt gun. The round that wrecked your gun might well have wrecked a bolt gun too, but b/c the bolt operates manually the lugs would not have rotated out of the locked position on firing. With the AR, a huge pressure spike makes for really high port pressure, violently forcing carrier back, unlocking gun too early. The reason case heads removed after AR KBs curiously look "belted" is b/c the case head lets go after the bolt unlocks and starts to move back. While in battery the head was supported about as well as on a M700 Remington. The problem is that it couldn't stay in battery long enough. Brass is ductile and expands like crazy once unsupported given enough pressure.

Sam

Link Posted: 1/15/2006 10:56:52 AM EDT
+1 what Samuel_Hoggson said.

The case expands radially outward at the join where the bolt and the chamber meet. Thus the "belted" look, or in many cases, complete separation of the case head. This sounds like a typical high pressure Kboom.
Link Posted: 1/15/2006 1:02:10 PM EDT
[Last Edit: 1/15/2006 1:10:58 PM EDT by Crowcreek]

Originally Posted By cmjohnson:
The swollen case can also occur if the system unlocks, comes out of battery, and starts to extract the shell TOO SOON, while pressures are still high. The round would have fired IN battery but the results LOOK like an out of battery firing accident.

The question is, WHAT can cause an early unlock and extraction?

I'm SURE you shouldn't be reloading .223 brass six times! Three times is my limit and then I whack the shell with a hammer and throw it in the brass to be recycled for cash bucket.


CJ



NOTHING can unlock it early -- But this is getting closer to the truth. The unlock is timed by the bullet passing the gas port. However, the pressure is supposed to drop before it unlocks, which again is timed by the bullet. If the bore is not clear by the time the pulse unlocks the action, the residual pressure will cause the damage we see here.

Not an out-of-battery, brass failure, overload or detonation, etc. IMHO


ETA: Point being, the bore was obstructed by a bullet jacket, foriegn object, unidentified object, or the previously fired slug or portion of that slug -- Whatever. There was enough residual pressure in the barrel to blow the partially extracted brass. That's a lot of hot gas -- enough to do all this damage.

A full- scale detonation, in the case of overpressure/overcharge/caseneck would have shown more damage in he barrel/chamber area.
Link Posted: 1/15/2006 1:23:07 PM EDT
[Last Edit: 1/15/2006 1:30:13 PM EDT by Crowcreek]

Originally Posted By Samuel_Hoggson:

Originally Posted By papajohn:
Could an over-long case keep the bolt from locking up properly, yet still allow the rifle to fire?
Papajohn



More specifically, an overlong case neck. Not only could a KB result, but this is my best guess as to what happened. If the bullet is forcibly crimped on chambering b/c of excessive case length astronomical pressures can result. This is merely one type of high pressure overload. A primary failure of the case head (eg. improper annealing) is possible, but rare. Had you been using a bolt gun you might have noticed the increased resistance to closure on the round that KBd.......but, of course............

ARs do not fire OOB, but case heads do rupture when unsupported. The reason the OOB myth persists is b/c folks forget that the AR is not a bolt gun. The round that wrecked your gun might well have wrecked a bolt gun too, but b/c the bolt operates manually the lugs would not have rotated out of the locked position on firing. With the AR, a huge pressure spike makes for really high port pressure, violently forcing carrier back, unlocking gun too early. The reason case heads removed after AR KBs curiously look "belted" is b/c the case head lets go after the bolt unlocks and starts to move back. While in battery the head was supported about as well as on a M700 Remington. The problem is that it couldn't stay in battery long enough. Brass is ductile and expands like crazy once unsupported given enough pressure.

Sam




I'm sorry to have to disagree here, but dealing with overpressure/blown cases is a primary consideration for military rifle design. If the AR was capable of this, I'd consider it a design defect.

This looks like an unusual 'obstruction' situation. Perhaps there was something stuck in a flash hider?


ETA:

A PRIMARY design consideration IS the moderate pressure loadings for the semi's. And I have NO specific understanding of the AR style rifle.

Can you provide more information about the 'pressure spike'. Is it even possible?

Link Posted: 1/15/2006 2:36:18 PM EDT
Link Posted: 1/15/2006 3:19:07 PM EDT

Originally Posted By Crowcreek:
Can you provide more information about the 'pressure spike'. Is it even possible?




Let's start with Papajohn's description of the bolt/BC being forced violently backward. Had there been an obstruction proximal to the gas port there would be no unlocking, correct? B/C there would have been no gas to move the carrier, correct? As in a M700 Rem, or whatever. Lugs could have sheared, but this does not seem to have happened here. Ever notice that case remnants from similar high-pressure AR KBs often show evidence (the telltale bulge, or "belt") of bolt movement/unlocking?

Yes, 80,000 to 100,000 PSI would do just fine. If the chamber has a near deathgrip on the bullet b/c of failure to trim you can get such numbers. And the bullet will usually exit the muzzle. OTOH, if the pressure is high enough, there will be a burst barrel.

Obviously, the classic mechanical obstruction, "cleaning rod section left in the bore", type of KB can wreck a gun, too.

The fact that Papajohn can account for all his shots on paper argues against an obstruction past the gas port.

Sam
Link Posted: 1/15/2006 4:06:09 PM EDT
[Last Edit: 1/15/2006 4:15:06 PM EDT by ar-wrench]

Originally Posted By Samuel_Hoggson:


The fact that Papajohn can account for all his shots on paper argues against an obstruction past the gas port.

Sam



He does mention an odd hole in his target.

"The 2nd round kaboomed. The bullet struck the target low and 4 inches left of the first, with a small curly tail under the hole, but the hole was perfectly round."
Link Posted: 1/15/2006 4:33:23 PM EDT

Originally Posted By ar-wrench:

Originally Posted By Samuel_Hoggson:


The fact that Papajohn can account for all his shots on paper argues against an obstruction past the gas port.

Sam



He does mention an odd hole in his target.

"The 2nd round kaboomed. The bullet struck the target low and 4 inches left of the first, with a small curly tail under the hole, but the hole was perfectly round."



Sounds to me like the most odd aspect of the hit was POI. Moreover, shooting through an obstruction = no "perfectly round hole". I doubt you could get any mark on paper, unless shooting from something like 20 feet.

Kinda wonder what the muzzle velocity might have been??

Sam

Link Posted: 1/15/2006 6:03:48 PM EDT
I'm VERY inclined to rule out the barrel obstruction theory, because the rifle bore was clean and dry until the first shot, which hit EXACTLY where it should have. After examing the fired case, which was fine, I fired the second shot. It's possible the second bullet started coming apart in the bore from an overpressure condition, but the fact remains it still hit the target about four inches from the first hole, at fifty yards. I think it's more likely that the higher-than-normal velocity overstressed the bullet to the point of rupturing, but it still made it to the target nearly intact. Were it not for the little "tail" under the hole, I would not think much about the condition of the slug at all.

And while it's possible the brass was overly long, I sorted this batch of brass in an L. E. Wilson headspace gauge, anything that was too long got pitched, or so I believe. All my loaded ammo is also checked with the gauge, or at least most of it has been. I guess I'll go back to using my Oly Match Heavy-Barrel upper for further shooting, with a new bolt and carrier. I just wish the was something obvious to point my finger at as the cause. I just examined the bore and chamber with a good light, and there's nothing to see but unburned powder residue. The chamber and lugs look dirty, but normal. It's still an unsolved mystery, as far as I'm concerned. And a damned expensive one at that!

Papajohn
Link Posted: 1/15/2006 6:25:39 PM EDT
Papajohn, I'm not putting too much faith in the bore obstuction theory myself, but I can't believe the rifle fired out of battery, and I don't think overpressure would begin the unlock cycle before the slug exited the muzzle.

I will go this far with the overpressure theory (which does not rely on 'untrimmed brass' as a sole culprit):

It does seem possible - with a overpressure situation - for the base of the brass to 'blow' just before the slug exits the muzzle. If it was timed right, unlocking and extraction could occur a split second later, explaining the 'out of battery' pressure signs.

In the last 30 or 40 years, there have been many KB'd rifles, usually bolt-action w/ reloads, which have defied explanation. Most of these have involved reduced, or moderate loads of medium/slow burning powders. There's no reason it couldn't happen in an AR, but for some reason I suspect a more obvious cause.
Link Posted: 1/16/2006 7:04:55 AM EDT
What condition are the bolt locking lugs in? Any chance that the bolt failed?

When was the rifle last headspaced?

Anybody live in St. Louis that has a camera? We need pics dammit! BSW
Link Posted: 1/16/2006 2:03:46 PM EDT
Bore obstruction.

Hotgun
Link Posted: 1/16/2006 4:00:59 PM EDT
Let me give this event a new theory.

Papajohn seems to me from his post to be capable reloader.

When I started reloading I made some startling discoveries as to what you will find in cases that were prepared for loading,

First I found a 22 rim fire spent case in a 30.06 case that was ready to be loaded.
I found a paper staple in a 357 case.

I also found after loading some 38 pistol rounds that at least one had media left in it. When I opened the cylinder and extracted the cases I found several pieces of polishing media in my hand from the fired cases.

Powder changes from a solid to a gas and does its job,That media don't follow the bullet out of the barrel The gases expand and move along. It is possible that pappajohn may have had a case with particles that lay in the bore until he fired the second round.

The pressure required to do the damage is clearly caused by the bullets movement being interfered with. If the case ruptured with a clear bore the gas would vent and blow the mag perhaps but not the damage pappajohn states.

I'm more careful now to make sure there is no gremlins lurking in my cases.


My 2$ Glad you are safe papajohn. Be safe,,,,,,,,,,,,, Jim
Link Posted: 1/17/2006 12:43:45 PM EDT
Argggghhhhh..........

We have incontrovertible evidence that PJ's gun KBd after unlocking. The evidence is a ruptured case head - and intact lugs and chamber. How in heck could the case rupture if it wasn't under pressure? How in the heck could the chamber be intact if the case ruptured while the action was fully locked? If the bullet - or something - weren't still in the barrel how could the case head have been made to rupture?

Think about it.

Now, if you're still with me, let's go further: what do you think would have happened if this round had been fired in a gun that had it's gas tube disconnected? Answer: either the lugs/chamber/barrel would have held (= no KB, no unlocking), or parts would not have held (= KB). In this case, though the KB would have involved sheared lugs, ruptured barrel, ruptured chamber..........one, some, or all of the three.

The reason some of you have trouble seeing what happens with a high-pressure KB in an AR is b/c you're viewing a dynamic process with static vision. Under normal circumstances the gas operated AR does not unlock until the bullet has left and pressure has dropped. Yes, we all know this. Please listen to what I'm going to say: this was not a normal circumstance. Whether due to excessive case length........or whatever...........this was not a normal circumstance.

If you have an AR close by this is a good time to take out bolt assembly. Now, put the lugs in the locked position (carrier all the way forward). Next, start to move the carrier backwards, as occurs in normal operation. You just noted that the carrier moves a bit before the lugs start to rotate. Ahhhh..........the word we're looking for is "timing".

All automatic cartridge weapons must be timed. All of them. Period. Doesn't matter whether they're recoil, delayed roller, direct gas, op-rodded, eieio........whatever. All systems use cartridge energy - whether as recoil, or as diverted gas. This energy - in whatever form - must be used to move parts of defined mass. It is the job of the designer to make sure the gun stays locked until the bullet leaves and pressure drops. But the designer also has to be sure the gun will actually work. It must cycle. What to do? Answer: design the gun to function properly within certain a pressure/energy/recoil range.

Now you all understand that a pressure overload of your Ruger 10/22 can result in a case failure. We see the same thing, from time to time, with MACs and Uzis. The case would fail during opening. If pressure were somehow much, much more excessive the chamber could KB along with the case before much movement had occurred.

Now let's look at a gas gun. What do you think would happen if you made a bolt/carrier assembly entirely out of titanium. Let's throw in a very soft recoil spring. And just to show you what a nice guy I am let's install this in your AR (not mine) and use plain Jane factory ammo. Right, we won't specify a pressure overload. What do you think would happen? Right. Early-opening and possibly a case head rupture. Why? B/C the system was improperly timed resulting in premature opening.

Back to PJ - no he didn't have a titanium B/BC, but he most certainly had an over-pressure situation. Result was too rapid movement of bolt carrier with consequent unlocking before pressure had fallen.

And now you know why guys like Stoner aren't dummies.

Sam
Link Posted: 1/17/2006 12:53:33 PM EDT

Originally Posted By Samuel_Hoggson:
Argggghhhhh..........

We have incontrovertible evidence that PJ's gun KBd after unlocking. The evidence is a ruptured case head - and intact lugs and chamber. How in heck could the case rupture if it wasn't under pressure? How in the heck could the chamber be intact if the case ruptured while the action was fully locked? If the bullet - or something - weren't still in the barrel how could the case head have been made to rupture?

Think about it.

Now, if you're still with me, let's go further: what do you think would have happened if this round had been fired in a gun that had it's gas tube disconnected? Answer: either the lugs/chamber/barrel would have held (= no KB, no unlocking), or parts would not have held (= KB). In this case, though the KB would have involved sheared lugs, ruptured barrel, ruptured chamber..........one, some, or all of the three.

The reason some of you have trouble seeing what happens with a high-pressure KB in an AR is b/c you're viewing a dynamic process with static vision. Under normal circumstances the gas operated AR does not unlock until the bullet has left and pressure has dropped. Yes, we all know this. Please listen to what I'm going to say: this was not a normal circumstance. Whether due to excessive case length........or whatever...........this was not a normal circumstance.

If you have an AR close by this is a good time to take out bolt assembly. Now, put the lugs in the locked position (carrier all the way forward). Next, start to move the carrier backwards, as occurs in normal operation. You just noted that the carrier moves a bit before the lugs start to rotate. Ahhhh..........the word we're looking for is "timing".

All automatic cartridge weapons must be timed. All of them. Period. Doesn't matter whether they're recoil, delayed roller, direct gas, op-rodded, eieio........whatever. All systems use cartridge energy - whether as recoil, or as diverted gas. This energy - in whatever form - must be used to move parts of defined mass. It is the job of the designer to make sure the gun stays locked until the bullet leaves and pressure drops. But the designer also has to be sure the gun will actually work. It must cycle. What to do? Answer: design the gun to function properly within certain a pressure/energy/recoil range.

Now you all understand that a pressure overload of your Ruger 10/22 can result in a case failure. We see the same thing, from time to time, with MACs and Uzis. The case would fail during opening. If pressure were somehow much, much more excessive the chamber could KB along with the case before much movement had occurred.

Now let's look at a gas gun. What do you think would happen if you made a bolt/carrier assembly entirely out of titanium. Let's throw in a very soft recoil spring. And just to show you what a nice guy I am let's install this in your AR (not mine) and use plain Jane factory ammo. Right, we won't specify a pressure overload. What do you think would happen? Right. Early-opening and possibly a case head rupture. Why? B/C the system was improperly timed resulting in premature opening.

Back to PJ - no he didn't have a titanium B/BC, but he most certainly had an over-pressure situation. Result was too rapid movement of bolt carrier with consequent unlocking before pressure had fallen.

And now you know why guys like Stoner aren't dummies.

Sam



Holy fuck! Someone who actually knows what they're talking about showed up on Arfcom!!


<runs for cover, for the end is surely nigh>
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