Wow! That is enough pressure to blow that cap off w/o a bore obstruction.

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I remember running into one of those heaps years back.. So long ago it was still labeled Hesse. (SP)

Very much so. The pressure curve is such that although there's no way it would reach that peak it would still spike quickly enough to cause materials failure as seen. God knows what kind of powder and how much there was in the suspect SLAP rounds.

Quite likely any brand would have Kaboomed with bad enough ammo.  The difference is other designs arguably can be stronger, and more importantly, designed with the realization that Kabooms can and do happen; and take that into their design approach.  

Here's a Kaboom report from TFB, on a Bushmaster version.   I'm sure Barret is similar, in that they have a more conventional design which will catostrophically fail in a manner that does try to kill the operator.

I'm starting to suspect that your user name is a damned lie.

I don’t know anything about these rifles or this ammo. But when I seen the cap was hand tight it seemed dangerous. The design didn’t install much confidence.

I'd love a Mauser 98 action in 50 BMG. Given that the 50 is proportionally similar to 30-06, it should be possible. Maybe 35 pounds or so, plus a period looking bipod?

Yeah. We can call it the T-Gewehr.

Dad owned a Vulcan AR for a while. Complete pile of shit. The BCG was machined off axis, resulting in one of the 'rails' at the bottom being cut to a razor edge, and the other being way too thick.

It did have a neat fixed stock though, with kind of a hook like a Magpul PRS. We should have kept the stock and thrown the rest of the gun in a lake.

Yes, but with a box magazine.

The reason threads need to be tight in most applications is to prevent them from coming loose and falling out over repeated stresses or vibration, not to provide substantial linear strength.

Your bolt action doesn't need to be closed with a breaker bar for the same reason.

It seems that many here have the attention span of an autistic gnat and are un-interested in learning or actual facts.

And if it does need to be closed with a breaker bar or other lever - stop. Something is badly wrong.

Who is making/selling counterfeit SLAP rounds?

Tony

Realistically as long as the threads are not of some horrible tolerance or the steel too brittle when the pressure is applied the threads will deform and begin to distribute the load across them.

At least a handful of people. You'll also see counterfeit M855A1 and M80A1 rounds pop up. Counterfeit Mk211 "Raufoss" are also unfortunately common.

With any firearm, you have bolt thrust.  This is the peak force of the case pushing back on the bolt (think of the cartridge case as if it were a piston).  The following is the force for common rounds:

9mm - 4,000 lbf
5.56 - 7,000 lbf
50 BMG - 27,000 lbf

The clamping force is basically the force that opposes the bolt thrust so that you don't have a kaboom.  This is provided by the lugs/threads in your bolt/cap.  Shear stress = force/ area (of the shear surface).  When shear stress > Yield strength, things break.  While by rough eyeball, the area of the shear surface on the RN50 looks like it may be 2X that of the barrel extension on an AR, what Mr Wannabe Engineer forgets is the bolt thrust is nearly 4X as much.

Also Mr Wannabe Engineer is clueless as to the how mass plays an important role in a dynamic system.  Let's imagine you have the same nonesuch cap design for a 9mm rifle.  Putting aside factor of safety right now, that lightweight cap needs threads that withstand ~ 4,000 lbf so that it doesn't kaboom.  However if you add mass to the bolt/cap, the inertia of the mass resists the bolt thrust (Newton's 1st law).  If you add enough mass, you don't need any threads at all.  The bolt is so heavy that by the time that bolt thrust pushes it back far enough to expose the case, the pressure has dropped to a safe level so it doesn't rupture.  Thus this is how blowback guns work.  Although you would not want a blowback 50 BMG, the added mass of a large bolt is definitely better in the event of a KB than a tiny cap that essentially becomes a very good projectile.  With a proper design, you should have containment which all 50s have except these bare bones budget 50s.  Anybody who would equate the danger of shooting an overcharged round in a RN50 to a M2HB is an idiot who doesn't know what he's talking about.  The bolt group on a M2 is massive as is the thickness of the receiver walls and backplate.  I would take standing behind my M2 or my Barretts any day of the week and 2x on Sunday in the event of a KB over these crap 50s which provide an easy path from the bolt/cap to your face.

ETA: Fixed formula which I had inverted

Clamping force with a bolt action will be insignificant as the lugs are not preloaded much when closed on a round. Or maybe I'm misunderstanding what you mean by clamping force.

Also I don't see how clamping force plays much in the role of a what is essentially a pressure vessel design with a cap (lug or threads) assuming proper headspace.

I don't know how to state it any more simply than I already have

You're supposed to say "I'm an engineer not a communications major."

Zastava Black Arrow is exactly what you are looking for.

Awesome.

Yeah I are enginear too (mech) and usually I understand other speak speak fine. Granted its been a while since college and i dont deal with exact field.


Im just trying to understand how treating chamber as a bolted joint when figuring out shear strength of lugs or in this case threads applies.

Should be: shear stress = force / area right?

Great explanation, thanks.

I don't think you can. It was very clearly written.

Shooting ammo of unknown condition, especially in high power cartridges, is not very intelligent. Especially in gimmick weapons.

User is lucky to be alive......hopefully lesson learned....

Where in the world did you go to school?  It's not that hard man.  Clamping force = longitudinal force of a pressure vessel.  That force is provided by the threads in the cap.  Stress = force/area  The greater the area of the threads in a cap or barrel extension, the lower the stress.

Doh, yes F/A, thanks.

just out of curiosity what would the bolt thrust be at 85,000psi

Ill be wasting some time going though the first link I found looking, someone took the time to do an finite element analysis on a rifle action. Also found dan lijas comments on lug design interesting.

http://www.varmintal.net/abat85.htm
https://riflebarrels.com/a-look-at-bolt-lug-strength/

Not entirely true, as rocketman mentioned.

Threads aren't perfect. Tightening them to an appropriate torque figure forces a more complete engagement with all of the thread surfaces. Thus preventing one or two threads from taking the initial load and starting to fail, causing a cascading failure.

In a lug situation, the entire lug is bearing the load, even without 100% contact. Of course, the more surface contact the better.

~42,000 lbf

I get all of that except for using the term clamping force in that manner.

Cal Poly pomona grad but then i guess thats why we were always a step behind teh slo guys in rankings

How would a press fit joint be figured?

Steyr barrels are pressed into the receiver

That's a function of elasticity and amount of overlapped volume.

So is an AK & HK but retained by a cross pin.

goddamn.

between that pressure and the volume of gas that round makes it really is a miracle that dude is alive.

You guys working on the assumption that the round was ONLY at 85kpsi are incorrect

All we know is the threads failed around that pressure

The round could have been anything above that.

I remember 10? 15? (or more) years ago seeing pics of a barret opened up like a scissor jack. Want to say the bolt exited the receiver and crumpled the shooters jaw...but it has been a while.

Who made these particular ones is a better question.  They may need some kinetic counseling.  

Dupity dupity dupe.

There are standard formulas using white supremacist math to determine holding forces with interference fit joints.  Not different really than spec'ing the strength required of a lug, bolt, or any other part.

Damn, my apologies!

Not the lugs.
The barrel extension is attached to the barrel how?  

Barrel extension attached to barrel how?

Yeah that was a hangfire using some Central American ammo IIRC.  Imagine what would have happened here if it was a hangfire and it went off while the cap was opened

This is actually untrue. Most reputable manufacturers design their rifles to survive up to 2x overpressure without detonating, and most have design features to not kill the user if it dos kaboom with 3-4x the pressure. For example desert tech has a video of them shooting one of their SRSs in 338 Lapua mag, and the proof load they use is a complete case full of a fast pistol powder. Like filled to the brim, with a compressed load. Thats probably 2-3x the safe pressure for 338LM, Gabe even more. They shoot it and the rifle totally held together, the only symptom being they had to Hamer the bolt open with a 2x4 and the case was destroyed.

Its possible that they were legit.  Slap ammo is old, most of It is from the 80s. Also a lot of it was stored in the hot, dry Mid East shitholes  where it was used. Corrosion and power degradation are pretty common in the legit rounds. Its also possible that the powder stabilizes decomposed and instead of slowing the burn rate detonated and accelerated it.
It could have been a questionable handled, but its surprisingly hard to that significantly overcharge a 50bmg case using standard powders

With a hell of a lot more thread engagement, and an actual torque spec, with a hell of a lot less bolt thrust, and also with a big hunk of cast or forged aluminum preventing it from traveling toward your face.

There is no getting around how bad this design is.