Blew up a gun Thursday... now tell me WHY?

[Char-Gar]

Actually slow machine gun ball powders like WC872 need some compression to ignite and burn decently.

[DrB]

While undercharging increases the possibility of SEE, it by no means is a mandatory prerequisite of SEE. At BRL we saw SEE (in admittedly larger guns) in different circumstances, including too much primer and not enough primer. SEE in its essence is an undersired transition of an energetic material from deflagration (burn rate) to detonation (explosion). Any number of circumstances can cause this transition.

What gets my attention is that the OP had just upped the load slightly and may have created a compressed load. Compressed loads of ball powder are slower to ignite, since there is not as much air space for the primer flame to propogate. They also create the possibility of primer induced debulleting, creating the dreaded start/stop/start motion of the bullet. Such a situation may not need to induce SEE to blow out rifle brass; a weak old case and a single instance of boolit stop/start may cause enough of a pressure excursion to create the damage done without an actual SEE event. (See my previous post on damage).

HF

Thank you! I assumed we were discussing deflagration/ detonation transition with SEE, but I have never come across a rigorous physical discussion of the how/why wrt SEE. Usually folks talk about the powder incompletely igniting, setting forward to the case neck and going boom, which is rather vague.

There was a point (ref PO Ackleys books) where the powder manufacturers were in vigorous denial of the possibility. Over the last few decades they seem to have acknowledged the possibility with low capacity charges of slow burning powders... I haven't seen any acknowledge the possibility in full capacity charges (not that that necessarily means anything).

If you have anything more re SEE det wave formation I would love a PM on same.

[waksupi]

I do not at the time have access at my finger tips, but NATO did an intensive study on SEE years ago, and did find it is real. Do some Googling, you may find it.

[Char-Gar]

SEE has been known and taught to artillary men for generations.

[303Guy]

I can explain how it happened, the primer pressure or initial pressure pushed the boolit forward where it stopped, increasing the volume and simultaneously dropping the pressure in the case so that the slow and heavily coated powder burned like it would in the open. By the time sufficient pressure had built up to burn it properly the retardant coating was gone and there was insufficient volume to absorb the now rapidly building pressure and simply put the boolit had now become an obstruction. Hence the over pressure. This is not a detonation although it sure looks like it!

Once the case head expanded between the bolt face and the chamber face it formed a large piston causing the high pressure to act on a large surface area resulting in the catastrophic overload on the action.

This type of blow-up has been replicated in the laboratory and happens exactly like I described. It was with the 6.5 Swede. The blow-ups did not occur with the load development barrel but blew up test rifles during the final testing phase before that ammo went on sale. The truth is, the use of certain very slow powders is very dangerous for that reason.

[DrB]

I do not at the time have access at my finger tips, but NATO did an intensive study on SEE years ago, and did find it is real. Do some Googling, you may find it.

I am satisfied it is real, there seemed ample reason even in ackleys day to believe either powder plugging caused pressure excursion or detonation transition. I will look for the nato pubs... Do you recall if they were agardograph articles or tr's?

Doubting that there is evidence of SEE in this instance, and wanting to understand better the physics of why in particular circumstances you would see a detonation wave form is not the same as doubting it can ever occur. It is a fact that both nitrocellulose and nitroglycerin will propagate a detonation wave. I believe it is also a fact that in small arms applications they typically do not significantly transition, despite being subjected to shock waves, impact, and shear while burning. I am both very curious about the circumstances in which they do transition, and sceptical that there is yet supporting evidence this occurred in this instance.

In this particular instance I don't see a reason yet to suspect a SEE detonation vs. deflagration. Seems to me that detonation might leave metallurgical evidence from the shock wave imparted to the chamber? Anyone with practical experience looking at actual SEE?

[Ben]

Ummm, I guess you wish that you'd been shooting the old time honored and proven load of 2400?

Ben

[felix]

Yes, RustyW's action was physically interrogated. Grain structure made it conclusive. ... felix

[lavenatti]

This may be a stretch but...

The broken locking lug on the bolt left a surface that looks like it's been corroding for a while. A little hard to tell from the picture, but that's what it looks like to me. Could this missing chunk have broken off, been left behind in the chamber and unknowingly pushed into the barrel ahead of the next round?

[sunnywayne]

sounds like a old .318 bbl

[sunnywayne]

.325 proj in a 8mm ? old brass ? old brass thats been reformed from old 30-06 brass ? mag primer ? next time use reg primer new brass made for 8mm mauser an a .323 proj if a modern bbl wc867 fill to top press proj in if that was a 98 it should have stayed together

[303Guy]

I don't know where I read the bit about the Swede ammo causing blow-ups but if one could find it that would answer the question as to how and why. It's not a detonation, it's simply a large powder charge burning too fast in too small a space and like I said above, the resultant pressure got to act on a large surface area causing the damage we see. That effect is known and understood and is why an otherwise strong action fails but that's a separate issue. This could be called this a SEE as the powder burn had entered into an uncontrolled state after initial ignition and became very rapid but it was still burning (or exploding) but not detonating and was simply an uncontrolled and irregular burn. I believe a detonation would have shattered the action and chamber. An explosion would be defined as a rapidly expanding gas.

[Larry Gibson]

DrB

My only problem with the suggestion of SEE is that it requires the assumption that an under charged case happened to occur on the second round, that an undercharged case was missed in a nominally FULLY charged case, and that SEE, which may or may not even occur with this powder/case/primer did in fact occur. Has anyone ever reported probable see with this particular powder?

A misassumption on your part. SEE occurs from an intentional reduced load of slow for the cartridge/bullet powder along with other conditions. In this case the powder charge was not "reduced" in the classic sense fo being less loading density as it was loaded to 100% loading density. It was "reduced" in the sense that the burning rate was way too slow for the case capacity even at 100% loading density. There is nothing in the conditions for an SEE that requires the preceeding round be an "under charged" load. If you read the Handloader article describing the laboratory reproduction of an SEE event you will see what the pre conditions are. I have posted that article numerous times and a search should easily find it.

An event with the second round seems a bit of a coincidence to me. Was the second round fired the second round loaded? Second to last? Unordered with respect to loading vs. firing? The nominal load was a case FULL. Were ANY incidents of under charging observed among ANY of the charges thrown (both observed and corrected OR upon disassembly?). Have you observed/corrected under charging with your setup with any frequency (or ever) with these powders?

As already mentioned all conjecture there is moot as the second round was not and need not have been "under charged".

If you have a history of undercharging, SEE becomes more plausible on just the second round fired, especially if anyone else has ever observed it with wc867. If no one has ever encountered it before, and there is no history to point to a likely undercharging, SEE becomes a possible but improbable theory.

Another question... is the assumption of a special cause such as SEE necessary? Given the dearth of load data out there for this cartridge and wc867, and the lack of a gradual load work up in this instance, does anyone KNOW that this particular charge, chamber, primer, and bullet doesn't nominally produce excess pressures? It wouldn't be conclusive, but it would be interesting to know what QL predicts, or even better mean and sd pressure profiles such as would be worked up by a serious load publisher.

Because the powder used, 867, is extremely slow burning it would be ill advised to further reduce it to "work up" the load as that is then intential under loading and/or reducing the powder charge to a more probable dangerous level and would then really set the stage for another SEE.


It would be nice to conclusively discount the nominal gross over pressure scenario... as if it is what is expected to occur with this load it is likely to bite the next one of us who tries something very similar to the OP. Given the general discussion online about these powders and the apparent assumption that these powders can't be overloaded in cases smaller than 50 bmg, any of us who ignore the usual work up from known starting point rule may be in jeopardy if our assumption is mistaken.

So is the assumption well founded that wc867 + magnum primer can't develop excessive pressure in 8x57?

Obviuosly since the first 2 shots jonk fired exhibited no signs of excessive pressure that assumption can be made. The question, each time one pulls the trigger in any test to prove your assumption, is whether the magnum primer will sufficiently ignite the powder to give the bullet a continual movement down the bore? Or will the magnum primer merely push the bullet into the throat where the bullet "sticks" and then the powder begins to burn before the bullet gets moving again and creates excessive pressure? That is the question isn't it? Perhaps, in my humble estimation, it would be far more prudent to stick with appropriate powders for the cartridge/bullet at hand, ya think?

However, I for one am not going to test your theory. The evidence is quite clear here. Feel free to "conclusively discount the nominal gross over pressure scenario" by conducting your own test of your theory/question and prove me wrong if you'd like...........but I shall have none of it for I have already been directly involved with 2 SEE's and am not entertaining a 3rd.

Larry Gibson

[Larry Gibson]

I don't know where I read the bit about the Swede ammo causing blow-ups but if one could find it that would answer the question as to how and why. It's not a detonation, it's simply a large powder charge burning too fast in too small a space and like I said above, the resultant pressure got to act on a large surface area causing the damage we see. That effect is known and understood and is why an otherwise strong action fails but that's a separate issue. This could be called this a SEE as the powder burn had entered into an uncontrolled state after initial ignition and became very rapid but it was still burning (or exploding) but not detonating and was simply an uncontrolled and irregular burn. I believe a detonation would have shattered the action and chamber. An explosion would be defined as a rapidly expanding gas.

It's in the Handloader article I've posted numerous times, a search should find it for you.

It is in http://castboolits.gunloads.com/show...ght=Handloader

Post #131

Larry Gibson

[nanuk]

I still get confused when I read that you cannot use too slow a powder if the case is full, as opposed to too fast.

I mean, take a case like a 30-378wby, or a big Lazz... Wby with the long throat, it would be very easy to replicate the events.

There is lots of contradictory info out there, for us less experienced handloaders.

ones like myself need to pay heed to what the more experienced guys like Larry G et al, and learn slowly.

because some things seem counterintuitive, or contradictory, it really does pay, to pay attention in class.

I do a lot more question asking relating to theory than I do experimenting, cause I know I still have a lot to learn

[SciFiJim]

I do a lot more question asking relating to theory than I do experimenting, cause I know I still have a lot to learn

Perhaps, in my humble estimation, it would be far more prudent to stick with appropriate powders for the cartridge/bullet at hand, ya think?

Larry,
I give great credence to your advice because of your experience is vastly greater than mine. However, it will never stop me from asking "WHY?" Accepting the advice to use "appropriate powders" doesn't increase my field of knowledge. I have been following the thread hoping someone would explain just why a full case of a slow burning power like 867 would cause the OP's experience. I still want to know WHY and HOW and under what circumstances it is a bad idea and when there is room for experimentation.

[Pigslayer]

Wow!! Reality check here! Nuff said. Glad you're still above ground.

[perotter]

Jonk,

Thanks for updating us as to what happened.

[swheeler]

See, duplexing can be dangerous! cheeeese KIDDING!!!!!!!!!

[TinCan Assassin]

I think I'll stick with 13 gr Red Dot for awhile. I like having a nose.