Serbu RN-50 explodes

[ghbucky]

I think at this point that I don't really care what the PSI was. I don't think that really matters. The crux of the issue is that a failure blows the energy to the shooter.

And honestly, his focus on finding out how much pressure it would take to blow his gun apart makes me think he isn't really an engineer that understands this stuff, just a hobbyist/machinist.

[edit] I don't get the idea that he ever really put thought into what would happen in a failure, its more along the lines of build it so strong that it can never fail.

In my world of IT, we design everything to not fail, but then we build other systems to handle when there are failures, because something will always fail somewhere.

[Aguila Blanca]

Originally Posted by ghbucky

And honestly, his focus on finding out how much pressure it would take to blow his gun apart makes me think he isn't really an engineer that understands this stuff, just a hobbyist/machinist.

I agree completely.

I also think he's crazy to be making YouTube videos and saying anything at all about this incident. He made a product that nearly killed a customer. If I were his advisor, I would be telling him to shut up and lawyer up.

[Bud Helms]

Varmint Al ... 'haven't heard that name in years. Last time I was there was something like '05.

[reddog81]

Originally Posted by ghbucky

In my world of IT, we design everything to not fail, but then we build other systems to handle when there are failures, because something will always fail somewhere.

That’s what I was thinking. When designing a gun you have to assume at some point in time someone is going to do something to cause the gun to go kaboom. It doesn’t matter if it’s 85,000 PSI or a Ukrainian engineer thinks it’s 165K. It might even take decades but it’ll happen eventually

[WeedWacker]

He made a product that nearly killed a customer.

This is not entirely fair. The rifle may have been engineered for standard ammo and was perfectly suitable for that purpose. KB introduced a round that was outside the spec of engineering. It's like blaming Dodge for a catastrophic failure that occurred during a high performance dyno on a modified vehicle.

[Pahoo]

Another example of God's hand, saving the day, regardless of what else on this earth. may be happening. ...

Be Safe!!!

[ghbucky]

This is not entirely fair. The rifle may have been engineered for standard ammo and was perfectly suitable for that purpose. KB introduced a round that was outside the spec of engineering. It's like blaming Dodge for a catastrophic failure that occurred during a high performance dyno on a modified vehicle.

It was an unmodified rifle, and the ammo from all appearances was off the shelf. Any theorizing that the ammo was the cause is without any evidence. There is just as much evidence that the threads were weak and therefore failed with standard pressure ammo.

The point is that in the event of a failure, the Serbu design directs the energy directly at the shooter. There is no 'fail safe' state in that rifle.

[HiBC]

I do not pretend to be engineer enough to interpret this data.

I'm just offering an example of finite element analysis of stresses in a rifle action as presented on Varmint Al's page.

I'm sure technology has evolved to make it a more powerful tool.

If anyone is going to make a low volume production rifle action, it would seem FEM through failure would be a good idea.

Anyway,I think its interesting. There are more examples of FEM on Varmint Al's page.

http://www.varmintal.com/abolt.htm

[WeedWacker]

It was an unmodified rifle, and the ammo from all appearances was off the shelf.

SLAP rounds are not standard pressure rounds which may be outside the spec of the design. Same could be said for older handguns and +P+ ammunition. This is the only example of one of these rifles having a kaboom and everyone is jumping in saying it's the fault of the design when there are too many factors to rule out any one thing.

[HiBC]

Ok.
But Mausers, Springfields, Rem 700s,Ruger 77s ,etc have all been blown up to the point the cartridge brass brazed the bolt in place ,the stock is blown to splinters and the barrel splits like a banana peel

And the bolt does not get blown into the shooters neck. Thats 1898 Mauser technology.
That SERBU is designed around what is easy to make in a lathe.

I do agree,there are many complex factors at work. Not all of them will be apparent on a drawing board.The finite element analysis helps to understand the flow of stress in a computer model. I was exposed to it in Pro-Engineer software in the 1990's

I wonder how many SERBUS were tested to destruction to see how the shooter would fare.

No matter how high of a pressure a SLAP round may be loaded to,it really won't work out if the brass is pushed beyond the failure point.

I confess,I don't know much about SLAP rounds. Are they loaded hotter than blue pill proof loads?

[Aguila Blanca]

Originally Posted by WeedWacker

This is not entirely fair. The rifle may have been engineered for standard ammo and was perfectly suitable for that purpose. KB introduced a round that was outside the spec of engineering. It's like blaming Dodge for a catastrophic failure that occurred during a high performance dyno on a modified vehicle.

The point isn't that a firearm failed when exposed to a round that appears to have been massively over-loaded. The issue is that the design didn't provide for a "fuse" -- a point of failure that would blow first in a location and way that would not endanger the life of the shooter.

I'm sure we have all seen photos of revolvers that have failed. The almost universal mode of failure is that the top of the firing chamber opens up, usually followed by ripping open the top strap of the frame. Sure, the shooter's hand may incur some injury, but at least it probably won't be life-threatening.

Several people in this thread have made the point that the design of the Serbu didn't provide such a "fuse." The weakest link in the chain was the threads of the breech cap and, upon failure, that became a potentially lethal projectile. I don't think anyone has suggested that the gun should have been designed to withstand massive over-pressure. The point is that the design should have provided a way of directing massive over-pressure away from the shooter.

[WeedWacker]

The issue is that the design didn't provide for a "fuse"

This is a cop out. It was designed a particular way and someone used it outside of those bounds. The ears on the back should have handled to failure to a degree, but the pressure was so extreme even a third lug on a Mauser design wouldn't have stopped a bolt from flying through the back of the rifle. Things can be overengineered to a degree for instances when the product is used outside the design parameters, but we're talking about the contained force of a .50 BMG. The design objective of the RN-50 is an affordable .50 BMG rifle that can be operated safely with standard loads and it fulfills that role exactly. Now everyone is armchair quarterbacking a situation that approached pressures Serbu, let alone Barret or Lapua to name a couple big-bore brands, may not have tested for when testing failures.

To be perfectly honest, I would like to see the ammo that was part of the failure before passing complete judgement on the design. For all we know there was a weakness that could have had similar results in a different design.

[HiBC]

This is a cop out. It was designed a particular way and someone used it outside of those bounds.

We disagree

I believe in Murphy's law. If it can go wrong,it will. This case proves the point.

I have seen buttress thread type locking lugs on original Newton rifles.No place else have I seen 60 deg vee threads serving as the the locking surface.
Although,true,barrel to receiver threads are typically vee thread.

The breech cap is in the form of a cup. One end is open. The linear load on the threads ,by way of the vee,gets translated to a force that wants to open one end of the cup.
I don't pretend I know what happened. I don't even argue with the gun being subjected to abuse via the ammo.It DID fail. No matter how it failed, the breech cap becoming a projectile that nearly killed the shooter is unacceptable.
Its one thing if you hobby shop up your own gun and it blows up and kills you.

Its another if you are selling them. I'm curious how much "failure mode" testing was done. You know,"Crash test dummy" testing?

Maybe blow up 5 or 10 SERBUs with a watermelon for a shooter?

Were those "Ears" speculated to work or did they go through catastrophic testing? 5 or 10 times?

I get it ,the failure was not supposed to happen. But it undeniably DID happen. With near fatal results. You talk about "not fair" ? Thats not fair.

I'll agree,the ammo and chain of custody are unknown. It might have been dirty trick sabotage gun wrecking CIA ammo,

Its a bad design if the point of failure blows a hole in the shooters neck. Its not fair,

[Double Naught Spy]

This is a cop out. It was designed a particular way and someone used it outside of those bounds.

We disagree

I am of two minds on this. On one side, I feel that there is a limit to how much we can protect people from themselves. Just how many contingencies should a manufacturer incorporate into the design of a product to control for people doing what they should not do?

Sometimes, doing something stupid hurts. Sometimes, it hurts a lot.

What is interesting here is that let's say it was a misloaded round. How come nobody here is worried about going after that issue? Is it because nobody knows who it was? Then who was it that loaded a round of unknown origin into the rifle? The Serbu isn't chambered for SLAP rounds, but he managed to get it to chamber. In this scenario, there were at least two failures before the rifle ever failed and none were Murphy's law (or the folklore version we accept today as being Murphy's law).

In the other, I wholeheartedly agree that the design should be better.

-------------

As for the ears, I don't believe they were ever supposed to stop a catastrophic failure. Their purpose was to assure that the user actually had the cap screwed down fully before firing the rifle (as explained in the video). If the cap wasn't screwed down fully, it will catch on the ears and the gun not be allowed to go into battery.

[Radny97]

Originally Posted by WeedWacker

This is a cop out. It was designed a particular way and someone used it outside of those bounds. The ears on the back should have handled to failure to a degree, but the pressure was so extreme even a third lug on a Mauser design wouldn't have stopped a bolt from flying through the back of the rifle. Things can be overengineered to a degree for instances when the product is used outside the design parameters, but we're talking about the contained force of a .50 BMG. The design objective of the RN-50 is an affordable .50 BMG rifle that can be operated safely with standard loads and it fulfills that role exactly. Now everyone is armchair quarterbacking a situation that approached pressures Serbu, let alone Barret or Lapua to name a couple big-bore brands, may not have tested for when testing failures.

To be perfectly honest, I would like to see the ammo that was part of the failure before passing complete judgement on the design. For all we know there was a weakness that could have had similar results in a different design.

I think this analysis is incorrect. The gun should have been designed so that the barrel should have banana peeled (or some other part of the gun should have blown) before that end cap ever had a chance of coming off. That’s the crux of the design flaw.

I agree with Double Naught Spy that the ears do not appear to have been designed to deflect or redirect a failure, but just to ensure the end cap was fully screwed down.
If they were designed to deflect, then the design was doubly flawed, as the ears turned into their own shrapnel which almost ended him.


Sent from my iPhone using Tapatalk

[ghbucky]

Everyone seems to take it as a given that the ammo caused the failure.

How would this look different if it was a manufacturing flaw... say if the metal used for that gun was flawed in some way, or the threads gave up the ghost due to fatigue?

[Joe-ker]

Originally Posted by ghbucky

Serbu has posted a new youtube video yesterday. He is now saying that to blow that breach cap off is 161k+ psi.
https://www.youtube.com/watch?v=na1Qo7FxDeM

He's going with the "there is nothing wrong with my design" approach.

He is saying that it was a 'counterfeit' slap round. He apparently still does not have the rifle or ammo.

He does not at all address the plain fact that the shooter received all the energy when the system failed, regardless of the cause.

I agree. Terrible design.

[Ricklin]

Or blessed. Whichever it is he is happy to be seeing the green side of the grass.
The builder? Best hope his Atty. approved the video he posted.

My 64,000 dollar question? Two actually.
How can the builder state the PSI for this to have happened?
What was the percentage of thread engagement of the blown up rifle assembly?

Those questions are related, no? The rifle in question is older and well used per the shooter. What was the thread engagement of that rifle?
No horse in this race, fascinating overall. I think that regardless of what the builder chooses to do, he's screwed.

[stagpanther]

I remember when Mark was developing these things and was offering pre-production discounts. I was really interested and a local GS owner was also--he got one and I took a look at it, but the screw-on breech was the show-stopper for me. Even though I know squat about engineering I figured no way that was going to be the equivalent of locking lugs--and I'm not saying this just because of this one failure. It's true anything can fail--I have personally blown up 2 AR's, but they had a "graceful suicide" and luckily I escaped any injury (except maybe to my pride, what little I have).

[SC4006]

I see this thread has not been updated in a little while. Mark Serbu himself has posted three videos about the incident. The first is his initial reaction the the incident:

https://youtu.be/5AY6iEVhJE8

His second video he explains the strength of the threads used in the design:

https://youtu.be/na1Qo7FxDeM

His third video are his initial thoughts upon receiving the RN50 in question:

https://youtu.be/4ny_V_VfT3Q

[ghbucky]

I missed the updated video. Thanks.

The more that comes about this the more I want to be miles away from one of these rifles firing.

[Mike Irwin]

"How can the builder state the PSI for this to have happened?"

Materials modeling.

[anyrange]

RN-50 Thread Failure
As stated in this video ‘RN50 Accident Preliminary Analysis, on markserbu YouTube Channel” it was reported the force in pounds to fail the threads on the RN-50 was calculated to be 19,965 pounds of rearward force. Everything in the report is correctly stated for any fired round without case head separation. In Scott’s case, there was total case head separation. When total case head happens the ignited gas will also pressurize the rifle chamber. In most rifles and pistols the rear of the chamber is the exterior diameter of the cartridge case. The RN-50 has a screw-on cap with 1.5 in x 12 threads. So the rear of the RN-50 chamber has an area of 1.76 in². The calculated rearward force on the RN-50 cap when total case head separation occurs at normal pressures of 55,000 psi is 55,000 psi times 1.76 in² which equals 96,800 pounds of rearward force. The force that occurred during a case head separation is 1.65 times the force to fail the threads. Case head separation does occur has you mention and is more common with rounds used in automatic weapons with more headspace. I and lots of my friends which are across the course shooters carry case removal tools. However, most if not all rifles and pistols have some sort of ventilation system to redirect combustion gases away from the shooter when case head separation occurs. The RN-50? The only way I would fire one is using a long string.