50 cal explodes on video

[Lkwebb]

Here is a video TibasaurusRex put out explain his thoughts on exactly what happened...https://youtu.be/ardw09S7GfE

 

[DRNewcomb]

The two biggest take-aways that I've gained from this, so far.
1. Do not fire a sabot round through a gun with a muzzle brake, unless the sabot has been designed for and tested with that brake.
2. The cup breech on the Serbu has the property that when the cartridge case (obduration) fails, the breech is subjected to many times (~9X) greater than normal pressure. This would not be the case were it a plug, such as is used in large caliber artillery. The Serbu design appears to lack venting holes to relieve the pressure of a ruptured case or primer.

 

[davidjoe]

I think there are some valid points here:

I don’t follow much of his reasoning.

1) more tenon threads than about four wouldn’t add much strength.
** except for the fact that the longer cap would be attached to every one of them, and would have to be ripped in half before a partial release, if the theory is that the first four threads do all the work.***

2) threads form such a strong joint because a bolt will snap before the threads fail.
***except for the fact the tenon here looks perfect, minus all those super strong threads, though.****

3) We know it must be an over pressure round.
*** except Kentucky hasn’t chosen to show anyone including the analyst the brass, and a thoroughly trashed case head would need to be seen before decreeing over pressure, I think.***

4) we know it cannot be the gun because it had been shooting without failure.
***except that it is also true that in so many instances of fatigued metal, it works right up until it suddenly doesn’t.***

5) gas escaping the case from a rupture multiplies pressure or bolt thrust many times over.
*** except we haven’t seen the brass, and, is this conclusion consistent with bolt thrust or pressure where there is not even a case, just powder or bagged powder, to begin with.

 

[spencerhenry]

It seems that a thorough and proper examination of the destroyed gun would yield information to determine a cause. If it was barrel obstruction, it seems that would be simple to find.

 

[brokeasajoke]

I did not watch the entire video but what I wonder is what has this rifle been subjected to previously? Maybe this was the straw that broke the camel's back so to speak.

 

[Knotwild]

Who knows what happened, but it's fun trying to guess.

Some people just do stupid things (in this instance I am referring to shooting a fire hydrant with a .50 at relatively close range) and stupid things happen. I have a friend with a not so smart son who cut a steel target out in his shop class and shot it at 25 yards with a .270. The bullet is still in his leg lying next to his thigh bone.

We should all be grateful we live where everyone is free to do these stupid things.

 

[Old Navy]

Evidently the previous rounds were normal pressure since you screw the cap on and off with your hands. This gun is similar to the long gone Lone Eagle single shot pistol that was chambered for high pressure rifle rounds.

 

[std7mag]

When Lazzeroni did pressure tests using a Savage large action, it took 120,000 psi to permanently disform the chamber.
The action was still usable.

Rex from Sniper 101 believes the cause was the sabot running through the muzzle brake.
Backs his hypothosis up with book written for the use of the 50 cal.

Cool wits on part of Kentucky Ballistics. Glad he's still with us!

 

[Capt. Oblivious]

When Lazzeroni did pressure tests using a Savage large action, it took 120,000 psi to permanently disform the chamber.
The action was still usable.

Rex from Sniper 101 believes the cause was the sabot running through the muzzle brake.
Backs his hypothosis up with book written for the use of the 50 cal.

Cool wits on part of Kentucky Ballistics. Glad he's still with us!

Does he believe the Sabot got stuck in the brake?

 

[std7mag]

Pieces of sabot after repeated shots.
You can see the muzzle blast get larger with each successive shot.

 

[AllThingsAI]

Pieces of sabot after repeated shots.
You can see the muzzle blast get larger with each successive shot.

Muzzle blast can come from a broken or disintegrated plastic sabot. Gas and powder will escape out around the projectile. A blast from a 50 cal can easily destroy old plastic. An undersized tungsten penetrator bouncing down the bore is a recipe for disaster!

Just the engineer/machinest in me coming out, but that plastic sabot is orders of magnitude less strong than the breach cap. Any overpressure in the chamber should and would blow out the the plastic before it blows out the breach cap. In a way the sabot should have been a pressure relief valve (Like a freeze plug). BUT having an undersized projectile much, much harder than your barrel potentially bouncing down your bore...yikes.

Thank god Scott is still with us. Just a reminder to us all...slow down and think twice. There are usually tell tale signs before something catastrophic happens (as was the case here). Listen to those signs and stop, it's not worth dying over.

 

[davidjoe]

Muzzle blast can come from a broken or disintegrated plastic sabot. Gas and powder will escape out around the projectile. A blast from a 50 cal can easily destroy old plastic. An undersized tungsten penetrator bouncing down the bore is a recipe for disaster!

Just the engineer/machinest in me coming out, but that plastic sabot is orders of magnitude less strong than the breach cap. Any overpressure in the chamber should and would blow out the the plastic before it blows out the breach cap. In a way the sabot should have been a pressure relief valve (Like a freeze plug). BUT having an undersized projectile much, much harder than your barrel potentially bouncing down your bore...yikes.

Thank god Scott is still with us. Just a reminder to us all...slow down and think twice. There are usually tell tale signs before something catastrophic happens (as was the case here). Listen to those signs and stop, it's not worth dying over.

Yes, and also, with respect to the Tibosaurus video, it’s pretty certain he pointed out valid printed sabot-with-brake warnings, but the warnings comments don’t specify whether damage to the brake is the issue, a deflecting or tumbling bullet as it exits, or any other specific malady. That plastic building up could, at the brake or muzzle, severely over pressure the chamber so as to rupture it, may not be the right conclusion from those warnings, and Tibo seems to stop just short of saying it did mean that.

A reason maybe not could be that the sabot projectile would hit that obstruction at maximum velocity, about 4,000 FPS, and imagine how dramatically it would have to slow down (rather than blast past), in order to reverse the already-lower chamber pressure, go back past peak, then well exceed peak, all while the tube’s full volume is now available to the gasses. Further, I believe all points closer to a muzzle’s would-be obstruction than the chamber, would experience higher pressure than the chamber, and those points didn’t burst. I have heard of cans and brakes being blasted off the muzzle without chambers being destroyed.

We also need to keep in mind that what’s different here apart from being filmed, is that it’s not merely that the chamber ruptured, that event is rare enough but not unheard of, but that here steel was fired backwards so forcefully.

But regardless, Tibo points out a valid warning about combining sabots and brakes, whether or not it is meant to imply that chambers can blow if disregarded.

 

[AllThingsAI]

Yes, and also, with respect to the Tibosaurus video, it’s pretty certain he pointed out valid printed sabot-with-brake warnings, but the warnings comments don’t specify whether damage to the brake is the issue, a deflecting or tumbling bullet as it exits, or any other specific malady. That plastic building up could, at the brake or muzzle, severely over pressures the chamber so as to rupture it, may not be the right conclusion from those warnings, and Tibo seems to stop just short of saying it did mean that.

The reason could be that the sabot projectile would hit that obstruction at maximum velocity, about 4,000 FPS, and imagine how dramatically it would have to slow down (rather than blast past), in order to reverse the already-lower chamber pressure, go back past peak, then well exceed peak, all while the whole tube’s volume is now available to the gasses. Further, all points closer to muzzle would-be obstruction than the chamber, would experience higher pressure than the chamber, and those points didn’t burst.

But regardless, Tibo points out a valid warning about combining sabots and brakes, whether it is meant to imply that chambers can blow if disregarded.

I agree entirely...the massive kinetic energy of a projectile at the muzzle would do significant damage to any obstruction located there (or else clear it). You obviously understand your physics. Hard to avoid F=MA, K=1/2MV2 and PV=nRT.

But to your point, shooting a discarding sabot through a muzzle device is very obviously bad. There is immense power involved with a 50 BMG round, not something to take lightly.

Sure would like to see a bore scope video of the breach and barrel, and also that brass case.

 

[carlsbad]

This guy is very likeable and props to him for being up and going so quickly.

I have a couple of technical comments:

1. I hope there is more margin in the design than he said in the video. He said that the manufacturer said it would take 80ksi to blow off the rear cap. I would want at least a 2x safety factor. My guess is that there is more safety factor than that. You really want the stresses below the endurance limit to avoid fatigue failure in such a critical application.
2. I don't think the round being super hot is the actual explanation. The only way that it could have been that hot is if they put the wrong powder in it and that doesn't happen in a commercial ammo factory. I think something partially blocked the barrel. Here are a couple of thoughts.
a. This is a Sabot round and very old. I don't have much experience with sabot rounds but wonder if part of the sabot could remain in the rifle. also he points out that the muzzle flash on one round was very large....i wonder if the sabot rounds could have been rapidly fouling the barrel so that the pressure built to extreme levels.
b. the round he fired immediately before the one that failed was an incendiary round and it didn't make it through the fireplug. cast iron isn't very strong and for that round to not make it through, I suspect something was wrong with that round.
c. he was having extreme accuracy problems, perhaps caused by extreme barrel fouling.

Finally, when he closes the breech on that last round, something flies forward. Anybody know what it is?

--Jerry

 

[jelenko]

something flies forward

Very interesting. It seems to be moving quickly.