Help me figure out if this is a slam fire or bad loading. KABOOM!

[longdayjake]

The compensator came with the gun so I'm not sure how much they cost but they sure do work.

Slamfire,

The bolt was indeed closed when it fired. I'm really starting to think it was a brass problem. I know for a fact that every round was loaded with the correct powder. I didn't have any powder for anything else even in the same room. The only other thing I can think may have happened was some really bad bullet setback that added just enough pressure to blow the base of the case.

 

[Slamfire]

My personnel experience with slamfires in the Garand mechanism consist of two out of battery, where one blew the back of the receiver off, and one in battery slamfire during standing slow fire. That one, I placed the round in the chamber, dropped the bolt, and the rifle discharged without damage. All of these occurred with Federal Match primers and the last catastrophic slamfire, which blew the receiver heel off, I had reamed all primer pockets to depth and individually hand seated the primers. All were well below the case head. It was at this time I decided the conventional wisdom that “only high primers and your worn out receiver bridge” caused slamfires was bunk, and I began to suspect that maybe primer sensitivity had something to do with the phenomena, even though conventional wisdom discounted that as a root cause.

I have had one slamfire with one of those more sensitive brass finish WSR in an AR, standing slow fire, the rifle was not damaged. My scorer that day, he had an in battery slamfire in his AR, standing slow fire, with a federal match primer. His rifle was not damaged. He told me he had another with federals and that was the last he used federals. The AR action, unlike the Garand action, the firing pin is fully retracted until cam down.

Slamfires are so rare that partially closed bolt slamfires in a Garand action don’t pop up enough to establish a pattern, I would be very surprised, but not saying it could not happen, that the gun discharged during cam down, and the bolt stayed locked. I am aware that military M14’s have a much greater headspace than commercial M1a’s. A bud of mine checked the refurbished M14’s issued to his unit, and they all swallowed a commercial field gage. That could be an aggravating factor.

The bolt was indeed closed when it fired. I'm really starting to think it was a brass problem. I know for a fact that every round was loaded with the correct powder. I didn't have any powder for anything else even in the same room.

You still have not mentioned the powder nor its age. I don’t want to discount the possibility of an over pressure incident due to aged gunpowder. I have written on this extensively, just search for “deteriorated gunpowder” and my name. Burn rate instability will occur with old gunpowder, I have experienced it with surplus powder that had a neutral smell. I have also posted pictures and accounts of blown up guns with old surplus ammunition. If you powder is surplus, or is around 45 years old, you could have had high pressures due to old powder.

Since you were firing a GI M14, a machine gun, which has a high dollar value, I would recommend that you never run cheap surplus ammunition through the thing. If you destroy the receiver, you will have made the BATF very happy, because one machine gun is permanently off their register. They won’t give you a freebie to replace it.

And this is a reminder to use the appropriate primers for this mechanism. You have an out of battery slamfire that knocks off the receiver heel, that is not repairable.







That last one, the shooter was using CCI #34’s, had verified the primers were below the case heads, but the cases were not sized correctly. He placed a round in the chamber and dropped the bolt on it.

 

[[email protected]]

I had a close call loading some pulled 223 brass that I picked up at a gun show a few years ago. It was a bulk purchase and I knew that they were never fired since they had still had the primers crimped in. This made me real relaxed when I did my initial case inspection, which caused me to miss the one case that had powder in it. The powder must have gotten wet or somthing since it was packed inside the case. It wasn't alot of powder and 24.5 grains of wc844 fit in the case with it. My powder cop die caught it on my progressive press. I fired the round and the powder burned the best that I can tell.
In reading your posts I picked up that your load didn't fill the case. I assume the brass was once factory loaded and the factory installed primers were still intact.

 

[Peter M. Eick]

I watched your video a bunch of times and would have to agree with what many have said. A high sensitive primer problem blew prior to being fully locked home. It really stinks and why I go to great lengths on my M1A's to make sure I fully small base size the cases, only use c-34 primers and manually check every round to make sure it is below the case head.

Even with all that I know it is a possibility and never feed a case into the guns unless from a magazine and try to be careful of where the gun is if a slam fire occurs.

I hope it did not damage the receiver too badly. You video looked like a lot of fun, but expensive!

 

[243winxb]

The bolt was indeed closed when it fired.

My guess also, by looking at your photo. Looks like the neck/shoulder is missing??

 

[Slamfire]

I don't think the bolt had completely locked when it went off

.

I am guilty of jumping to conclusions and not reading further. My first 30-06 out of battery slamfire, federal primers and last round in the clip, there was partial engagement of the bottom of the bolt lug with the top of the receiver lug recess, just about the location in this picture



That partial engagement was enough to delay opening, but the bolt gouged its way back, and there were gouge marks on the right rail as the bottom right rear of the bolt was pushed rearward. I think this delay reduced bolt velocity enough that the back of the receiver was not cracked off.

This did not happen on my second out of battery slamfire, with Federal Match primers, and the bolt knocked off the receiver heel.

It is very possible that you had enough bolt engagement that the bolt stayed put, but not fully locked, which would have resulted in a blown case sidewall. After all, the headspace in a military M14 is huge compared to commercial. I have never attempted to measure wall thickness in LC cases, but they are heavier and I will bet that the sidewall is thicker further up the case than with some commercial. I have weighed a number of Federal Match cases, and their weights went from 155 grains to 165 ish grains. LC Match is generally 175 to 180 grains a case. Let us assume that the bolt was going down, the firing pin tapped a sensitive primer, and it ignited, and the resulting pressure was enough to keep the partially engaged bolt in place. Given the large headspace of a military weapon and thin walled commercial cases, the side walls blew. This is all speculation of course.

This is a M1 carbine receiver, the manual calls the receiver bridge a "firing pin retraction cam" and I think that is just what it is. This is functionally similiar to the Garand mechanism, just easier to understand from the picture. As anyone can see, there is a lot of travel before the firing pin touches the retraction cam and until then it is totally unrestrained in its forward movement.





In terms of firing pin protrusion on these mechanisms, I conducted some tests with three Garand receivers and this highly sophisticated tool: A stick, a nail, and a spring.


Placing the spring loaded stick on the firing pin tang showed some scary firing pin protrusion.



Here at what should be the thickest portion of the firing pin retraction cam,


Some bit of the firing pin is extending forward of the bolt face.


Here, at the pencil line on the right lug, the firing pin is clear of the cam (receiver bridge) notch and is able to go full forward.



In terms of total bolt travel, when you look at just how much forward movement the bolt has without the firing pin tang touching anything, and even during cam down, how short and steep the tang surface is, it should be obvious that the retraction cam/receiver bridge is pretty ineffective as a blocking mechanism.



It is my considered opinion, after reviewing every American Rifleman magazine from 1957 to 2000, that the concept that the firing pin retraction cam (receiver bridge) is a safety device is an idea that sprang up in the early 60’s. What was happening was that Garands were finally getting into the hands of civilians. You could purchase a NM Garand if you went to Camp Perry, otherwise, they were very hard to acquire. With commercial primers and the sloppy reloading habits of bolt gunners (case neck sizing, partial case sizing) civilians were having out of battery slamfires. At the same time, Springfield Armory (the original located in Springfield Mass) and the M14 were in the fight of their lives against the AR15/M16. American Rifleman articles from that time, dismissed out of battery slamfires in Garands as being due only to “high primers and your worn out receiver bridge”. There is no acknowledgement of primer sensitivity. Primer sensitivity as a concept does not exist. They were not informing the shooting public about the peculiarities of this mechanism. Shooters of the period are unaware that military primers, which were not on the market, are less sensitive than commercial primers. They were not telling anyone about the criticality of full length resizing. There is also no acknowledgement that due to the design of this mechanism, it does not have a positive firing pin block, which makes incidental firing pin contact with primer possible prior to bolt lug engagement. In fact, they delibrately create the impression that the firing pin is blocked. The retired Army Ordnance Officers working for the American Rifleman, the ones writing these articles, had already taken a position against the M16 (which really upset the Air Force) and by misdirecting an inherent limitation of the Garand mechanism, were doing their level best not to put into the public domain anything which would aid the opponents of the Garand/M14.

As such, it did not matter as the M14 was taken out of service, Springfield Armory was shut down around 1968, and the NRA was punted out of the Pentagon in the FY 1968 budget when the Army stopped funding the National Matches and withdrew a lot of other financial and non financial support from the NRA. If you read the American Rifleman magazine of the period you can just feel the pain and outrage of the NRA staff as they wail about unjustice of these events. They were advocates of aimed, accurate fire. They thought they were doing God’s work. The M14 with its powerful 7.62 cartridge was their baby and the Army not merely repudiated the concept of aimed fire, the Army crapped them out and everything to do with that concept, into the sewage pipes of the Pentagon.

 

[longdayjake]

Yeah, the top half of the casing is still in the chamber. I have a remover on the way along with a spare bolt.

I don't have an exact date on when the wc846 was pulled, but we got a bunch of lake city brass with it that was marked '05. I assumed it came from these lake city cases. I thought about using the lake city stuff but it was really dirty and I didn't want to deal with crimped primers. Lesson learned I guess.

 

[Slamfire]

Yeah, the top half of the casing is still in the chamber. I have a remover on the way along with a spare bolt

.

If this case separated in chamber, given the ruptured case head and a torn case, this would clearly be a firing pin initated slamfire. The case ruptured and tore due to excessive headspace.

 

[blarby]

^^^^ Beat me to it. Of sorts.

Was trying to figure out how exactly this sequence of events went down.... the last few posts made it fairly clear to me at least.

Very sorry about the loss of the parts, looked like an otherwise fine firearm.


A last Question for slamfire : Does the last round in the magazine have any effect on the timing of operation, in this instance ?

 

[243winxb]

Military BALL POWDER® Propellants listed in order of burn rate

WC 846 7.62mm Ball M80, Tracer M62
WC 846S 7.62mm Ball M80, Tracer M62
WC 846 + CaCO3 7.62mm Ball M80

http://www.gd-ots.com/download/BALL%20POWDER%20Propellants.pdf I have to wonder what the difference is , if any? Military load data > http://www.tuffsteel.com/manuals/armyammodata.pdf Chapter 11

 

[Slamfire]

A last Question for slamfire : Does the last round in the magazine have any effect on the timing of operation, in this instance ?

I have never seen any test data to indicate one way or another. I would think that since the top round in the stack is under the most spring compression that the upper rounds might take more force to strip than the later and especially then the last. Theoretically that would mean bolt velocity for the upper rounds is slightly less than for the bottom bunch. But, in the big scheme of things, I doubt it makes much difference one way or another.

When you get to see primer sensitivity data, and the spread, in inches, between "all fire" and "none fire", slamfires are really all about primer sensitivity, and all the rest are just mitigating factors.

 

[blarby]

Excellent, and good to know.

I've actually reviewed most of the data you've provided over the years on primer sensitivity, and appreciate all of your work correlating it.

In short, there is a reason I use mil-spec primers in autoloading rifles, and seat the snot out of 'em !

 

[Slamfire]

The bolt was indeed closed when it fired

On another forum you stated the bolt was half closed. On that forum, the domaint baboons don’t believe that primers vary in sensitivity and thus have mostly discounted the idea that your slamfire was due to improper primers. They also believe the receiver bridge is a positive firing pin block. I read strange theories about you using belted cases!?, bolts breaking ahead of time, improper bolt heat treatment, etc, I find their theories bizarre, strange, weird and weirder.

I am of the opinion that your slamfire occurred due to a sensitive primer. Because the bolt was not fully closed the case headspace was excessive. Not only did the case head sidewalls blow, but the case separated in the chamber. High pressure gas release broke the bolt nose and split your stock.

 

[blarby]

I have a hard time understanding exactly where that huge ring could have came from if the bolt was fully closed. Something wasn't ! Or, you have a hum-dinger of a chamber problem, ta boot.


Please, PLEASe PM me the "dominant baboon" thread.... I have plenty of popcorn !

 

[Slamfire]

Take a look at the pictures in post 18. Case head protrusion is an extremely important dimension and one that action designers must take into account. I have not found tables or references with allowable case head protrusion, an absence that is very intriguing, because this measurement is more safety critical than the more commonly known base to shoulder measurement. As Chin says, in his excellent series, and shows in his pictures, very little cartridge case protrusion is allowable or the case side walls will rupture. Here in this post, you can see just how allowable case head protrusion is in the hundredth’s or even thousandth’s of an inch.

http://www.practicalmachinist.com/vb/gunsmithing/how-much-too-much-253193-print/

If memory serves from my proof house work with Remington, SAMMI generally recognizes .180 inch as being the maximum case protrusion for 30-06 and standard belted mag configuration cases. It is slightly less for most flanged cartridges and a few thousandths more for 222 / 223 based cases and most of the tubing makers keep there webs nominally higher than that for safety. There is some confusion to this with CIP partly due to the Delta ΔL inch to metric conversion problem but their standards are approximately the same. Savage holds their overall protrusion to about .130, Remington hoovers close to .150, Brownings A Bolt is .135 and Winchesters post 64 can vary from .125 to .140 depending on year of manufacture. These numbers are generally not available to the public but do show up in pirate copies of some of the field service manuals. Also, they mean very little as brass makers keep the webs much taller than this as a built in safety factor. An easy way to think about it is that the guns were built first and then everyone designed case's with webs tall enough to accommodate all designs. Now days new firearms must be designed to work around existing cartridges or in some instances new cartridges and guns are designed together.

Most rifles start out with cases sticking out this much, and if you remember, maximum allowable headspace, as measured by a chamber gage, is only 0.006". From this point, the case is only allowed six thousandth's of an inch extra protrusion or the rifle is unsafe.

Springfield 03



Mauser



Autopistols operate a very low pressures, and a surprising amount of case head is unsupported in some designs. But it works as long as pressures stay low. Bump up the pressures too much unsupported case sidewalls will expand.





I had a bud who loaded his 45 ACP cases so hot, that after resizing, they looked like belted magnums.

So, what I see in the pictures is case sidewall rupture near the case head. I am of the opinion that too much case head protrusion lead to sidewalls sticking out of the chamber that were too thin to support the highest pressure. Of course, they were strong enough to contain the pressure for a while, then expanded, as pressure rose, then ruptured as pressure rose too much. Brass can stretch, does stretch, but can’t stretch forever.

 

[Walkalong]

Most rifles start out with cases sticking out this much, and if you remember, maximum allowable headspace, as measured by a chamber gage, is only 0.006". From this point, the case is only allowed six thousandth's of an inch extra protrusion or the rifle is unsafe.

But that is because of case stretching and separations, not support at the body case head juncture, unless I am off base here. Correct?

 

[blarby]

Why is it I always learn more in KABOOM discussions than so many others ?

This is where the meat is. Failure BLEEDS insightful discussion. I'm getting some more popcorn.

 

[Cmeboston]

Pulled brass is brand new brass that is primed. At one point it was made into ammunition but in this case federal found a flaw of some kind that caused them to scrap it. When commercial rounds are rejected it is usually because of a small blemish on the brass of some kind. Usually a small ding in the wall of the case or minor discoloration. I got them from the same place we get our pulled bullets. I've shot thousands and thousands of them before without issue but never in full auto. Most of that brass ends up going to full auto shooters so I figured we would be okay. I took a lot of shortcuts with this brass because I assumed it was new. Lesson learned. Inspect every single piece of brass.

Did you neck size the pulled cases? I full length resize all my pulled brass, I just take the primer pin out of the die. If you don't neck size your neck tension will not be sufficient and would surly suffer from setback in a FA gun..

 

[Slamfire]

Most rifles start out with cases sticking out this much, and if you remember, maximum allowable headspace, as measured by a chamber gage, is only 0.006". From this point, the case is only allowed six thousandth's of an inch extra protrusion or the rifle is unsafe. [/quote ]

But that is because of case stretching and separations, not support at the body case head juncture, unless I am off base here. Correct?

I wrote earlier that I don' have a table of acceptable cartridge case head protrusion so I am assuming that the case headspace we measure is actually only a measurement of case head protrusion, and that for safety purposes. I could be wrong on this, that Go and No Go distance may combine case stretch and case head protrusion, but I think it is primarily there for case head protrusion. Forgive me, if in the future, if I ignore case head protrusion and use case headspace to explain case separations.

I have written extensively on my experiments with greased and lubricated cases, and now I don't think that base to shoulder distance is all that safety critical, as long as the case sidewalls don't stretch and cartridge case protrusion is fine. Here is an example of an advanced primer ignition, this mechanism was used in the Polsten 20mm cannon, and for it to work, it required heavily greased ammunition. As anyone can see, the shoulder distance is only important as an ammunition stop. Once the case stops moving forward, the barrel shoulder provides a hard stop so that the firing pin can hit the primer with sufficient force to ignite. After that, well as long as the case sidewalls are heavily greased, so the sidewalls don't separate, and the case head is kept within the barrel chamber as pressure drops, the mechanism is safe and will function.

Picture from Chinn Vol IV.



As you know, too much "headspace" will cause case separations. This can be a safety issue, but most of the time, it causes a malfunction and ruins the case.

This is one of the exceptions to the rule:



We reloaders are fortunate that the only thing we have to worry about is base to shoulder distances, but the gaging system is set up so that the most safety critical measurement, cartridge case head protrusion, is virtually invisible to us. As long as shooters don't monkey with receiver recesses, grind material off the back of the bolt lugs, or put a spacer between the barrel shoulder and receiver face, case head protrusion is something set and controlled at the factory. If you stick a headspace gage into a rifle chamber and the headspace is greater than the field gage, you have been rightly taught to take that gun to a gunsmith and have it checked out. The greatest danger of excessive headspace is not if the chamber shoulder got pushed forward *, but rather that the receiver seats have moved back or the lugs have compressed. Gages will tell you if something is grossly wrong, and excessive case protrusion is the grossly, gross wrong.

I have had debates with posters who are under the misconception that the cartridge case is a strong pressure vessel, that is, it is able to hold all the pressure of combustion, by itself, like a propane gas bottle, and that the barrel chamber is simply a means of aligning the bullet with the barrel. This is not true at all, and a read of Chinn's Vol IV blowback section shows just how important case head support is for automatic mechanisms, http://www.ibiblio.org/hyperwar/USN/ref/MG/ (keep this link) The fact of the matter, the case must be supported, and must be supported as much as possible, or it will rupture. The weakest portion of a cartridge case will rupture with as little as 650-700 psia, the strongest part, I don't know exact numbers, but I believe the case head will blow above 80,000 psia. However, the sidewalls just above the case head, the more of that outside the chamber, the less pressure it takes to rupture them. They taper, it is obvious once you section a case.

Picture from Chinn Vol IV.



* Actually, now that I think of it, if the barrel shoulder got pushed forward, something would be grossly, gross wrong. And that probably would mean that the barrel or receiver threads are failing and the barrel is shearing its way forward through them. That would cause a big Kaboom!

 

[Walkalong]

if I ignore case head protrusion and use case headspace to explain case separations.

I would say that is correct, and what I thought I was saying.

I have written extensively on my experiments with greased and lubricated cases, and now I don't think that base to shoulder distance is all that safety critical, as long as the case sidewalls don't stretch and cartridge case protrusion is fine.

Agreed, if the grease stops the front of the case from gripping the chamber wall after the whole round slides to the rear and stops at the breech face, it will not stretch near the juncture of the thick web vs thinner side wall, it will just blow the shoulder forward, "fireforming" the case to the chamber. I would assume this would catch up with a case eventually, but it would not fail due to stretching/thinning above the web and separating.

 

[AverajeJo]

Don't shoot reloads in full auto!! And must use 7.62 x 51 with crimped primers not 308... Sorry but I am glad that you are ok!