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Discussion Starter · #1 ·
Kinda long, but very worth watching. To me this screams to only use known ammo.

 
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He's just the last in a long line of injuries from some terribly designed and executed 50 BMGs. He never says what the gun was or how it failed. I'm glad he made it. Some don't.
 

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The Hog Whisperer (Administrator)
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Not the brightest bulb on the string, then.

Quick, limited reading suggests that these are a tight fit in any sort of 'conventional' chamber. If he had to force the bolt closed.....
 

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Waste of time. Might help if the OP started out by giving some info on what it was all about.
 

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He did, the posted video was an edited version of his video. The full video is at this link.

This is a magnified image of the failed threads on the chamber. You can see how the threads were sheared off. The manufacturer claims that it would have taken about 85,000 PSI to do that damage. I am not impressed with only 4 threads holding that cap on. I don't know how deep a thread of that pitch should be cut but they look kind of shallow to me.

101559
 

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That's the same failure as the first Vulcan 50s. Vee form threads don't attain full strength with less than a diameter engagement and are NOT the proper design for intermittent thrust loads.
That was a dumb idea to pull the trigger on that thing.
What is a SLAP round?
 

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Elk Whisperer (Super Moderator)
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A "SLAP" round is one that makes your rifle come from together and slap you in the face, arm, hand etc.

Yep, just what I'd want to be shooting 50BMG in is a rifle made out of "assorted pipe" with no obvious gas escape paths.

Darwin's theory of evolution at work.

RJ
 

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Discussion Starter · #10 ·
That's the same failure as the first Vulcan 50s. Vee form threads don't attain full strength with less than a diameter engagement and are NOT the proper design for intermittent thrust loads.
That was a dumb idea to pull the trigger on that thing.
What is a SLAP round?
SLAP - Saboted Light Armor Penetrators. There was a mention in a comment I saw on another site that this might have been a sabotage round meant to inflict this very type of damage to an enemy weapon. The video creator admitted it was MilSurp from some other country and that it was shooting very erratically. Another reason to know about the ammo you are shooting. In this guys video...he had commented that he had shot the weapon many..many times prior and had never had an issue. I definitely feel that this was an ammo and not a gun issue. If the threads on the insertion system had been stretched previously, it would not be able to be threaded and function properly. It is a poor design as if it does fail, the shooter will be on the BAD end of the failure. However...we as shooters don't anticipate our weapons to fail. JMHO

Back in the early 80's there were a couple of gunsmiths/manufacturers in my area that paired up and were making single shot bolt actions that they were adapting to both rifle and Silhouette pistols. They were some of the finest actions of that type I had ever seen and I had the pleasure of shooting a number of them. Because they were small quantity, they were way more expensive than I could afford at that time of my life. I wished I had bought at least one in rifle and pistol. They manufactured some of their own barrels and bought others.

They made a few in 50 BMG rifle and had actually created a handloading press to handload ammo for them. The 50 BMG Rifles were quite heavy, but still needed a muzzle brake...they initially copied a Kleinguenther brake, but had to stop because of a "cease and desist" order from them (Don't copy other peoples stuff). They switched to an old style brake that was used on US Military 76 mm guns. I guess those were not protected by any patents. Those rifles were awful to be around when being shot and the blast from the brakes would knock sandbags off of tables next to them. We wound up only allowing them to be shot on the furthest uncovered table at the range. Even with the Brake, I saw a couple of guys get "scoped" pretty badly...one was even warned he was too close prior to squeezing off his round. Ouch

Alas, both of those gunsmiths are no longer with us. They were both brilliant machinists and innovators. Neither could operate a functioning gunsmith shop though. They failed to supervise their employees and got a somewhat spurious reputation for repairs because of that. I had a rifle of mine one ruined as a teenager (right after my Dad died), that I could have fixed myself after I gained knowledge....a learning experience for me.
 

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I did not do any calculations on the threads myself, but in the video he relayed the that the manufacturer stated the cap should not have failed until 85 Ksi. The round is designed at 55 Ksi. That is only a 154% safety factor. That is pretty slim considering what the device is used for. That is really a minimum safety factor.

It says right on their site "The RN-50 represents the first time a production firearm has ever been inspired by social media."

As are many great things, shortly followed by someone asking his buddy to hold their beer.

I also really enjoyed the part where he realized the rounds were not firing correctly but decided to try one last round.
 

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This points up the importance of knowing-- THERE IS NO ONE WATCHING how firearms are designed, manufactured, advertised or sold. Nobody knows but the lawyers that find the truth but the cases are sealed and so the truth is hidden until a court order produces the "OSIs", Other similar incidence complaints. I know nothing about this case or this gun but but just a glance at the design tells me I'M not shooting it with any ammo, especially surplus ammo designed for a different gun!
For the first time in my life, there are guns too dangerous to shoot right out of the box.
 

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Elk Whisperer (Super Moderator)
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Realizing that's not a "nut 'n bolt" situation, but . . . . . .

If a nut (in this case "cap") is left loose and not seated (properly torqued) it will have a tendency to come loose at the first "loading" whether in a shear or stretch situation. Repeated stresses only weaken the fastener (cap and/or barrel in this case) to the point of failure. The picture of the "bolt" looks like the "nut" wasn't fully threaded.

Yes jack, we all know lawyers know more about guns and such than anybody else with the tiniest amount of sense.

RJ
 

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The Hog Whisperer (Administrator)
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What the round was supposed to be loaded to (pressure), what the chamber dimensions for that round should be, and if/whether the ammo had been stored in such a way that the powder deteriorated, are all unknowns.

I'd be curious just how the manufacturer "knew" what pressure the threads would hold. Did they get ahold of some proof rounds for .50BMG? Inquiring minds want to know... and yeah it looks a little cheesy to me, at best, as far as mechanical designs go.
 

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Lawyers just develop information and sometimes can expose it.
RJ perfectly describes what happens when parts are 'loose'. It is a 'nut and bolt thing', especially with vee form threads.
Excess headspace hammers the bolt, a loose barrel hammers the threads.
Thrust on vee threads expands a thin outer member and reduces effective engagement of the thread. I see a tapered thread engagement in the picture above. The first thread from the shoulder is about half depth showing a tapered 'lead' on the cap. It would takes closer examination to determine if the failure was a heat-treat issue, tolerance issue or high pressure failure.....or just a weak design with no margin of safety. That there is a design failure is demonstrated by the damage done to the human involved.
 

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The Shadow (Moderator)
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Discussion Starter · #17 ·
I did find that the rifles manufacturer said that it had to be at least 85K PSI interesting. That seems to me to be in proof round category? I do feel that the rifles design contributed to the shooters injury, but surely not the main contributor. After noticing erratic behavior or previous rounds...he should have quit using that round. JMHO

I have a Winchester 96 OU that is approaching 145K rounds. I have NEVER done one piece of maintenance to it other than some extractor stops. I own two replacement firing pins in reserve if ever needed. I have a High-Standard that was made at the same plant (Kodensha I believe)...that is super tight. Nikko also made a number of their models off this design which I have always thought were better than the Winchester 101.

I've never been a pressure lover and have loaded for shotgun and rifle at (usually) well below SAAMI Max. I did used to load a lot of Ruger Revolvers close to Max, but never had any pressure issues with them.
 

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May I suggest it was the gun in the process of failing by stretching the cap threads that caused the ammo to be 'odd'. A threaded connection can be calculated to hold a certain amount of tension stress. 85KPSI sounds suspiciously like such a calculation. .003 headspace throws that figure out of sight. A 20% stretch on 16TPI vee thread gives approximately .020 excess headspace. The round didn't have to be overpressured to wreck the gun under those circumstances.
The fragmentation of the gun suggest less than a strong design. Loading a M98 (even a '93) to the same levels blows the floor plate off, breaks the stock, loses the extractor, blows smoke in all directions BUT backwards. A styrofoam maniquin head behind it has speckles of carbon but no rifle parts in it.
A Rem M700 gets hard to open and blows a primer.
 
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I agree the guy was not the brightest bulb for shooting ammo that he had absolutely no idea how it was stored or handled, & commenting on how old it might be. Duhh!

And I have never shot a .50 BMG, so I have no experience, but in my guns I would have stopped when I felt the differences shot to shot in recoil.

That said (repeating comments above):

A) Very BAD gun design, possibly compounded by someone NOT machining to print!
a) A minimum of 1 diameter of threads is always reccomended (as referenced above). Better is 1.5 diameters. Only exception is jam nuts or things that aren't gonna kill you like the nuts that hold toggle switches in a pannel.
b) Fine threads are stronger than coarse threads. These are coarse.
c) Square threads (Acme, etc.) are better. If you look at a cross section of 60° thread forms you quickly see they make a ramp that forces the threads apart radially. That is why you see the thread tops smeared over & not completely sheared off. The square threads are evidenced in all breach loading cannon/naval guns with interrupted thread breachs, & all bolt action lugs I've seen. Oh yeah, square threads are also no where near as sensitive to the tolerance build-up between internal & external parts!
d) Evidence of the 2 undamaged threads @ the barrel shoulder indicate the pipe cap used as a breach cap had a very large champher or possibly a cylindrical leade in machined in it to facilitate starting the cap in place, therefore reducing the thread engagement. Bad design or machining.
B) There is no secondary pressure containing feature (ie bolt handle in a notch of the reciever) if the primary feature (threads/bolt lugs) fail. Those tiny aluminum fingers sticking up (that did the real damage to the shooter) just simply don't pass the smell test, & absolutely didn't pass the "test to failure" test! I do agree they would possibly keep you from closing the "action" IF the cap wasn't screwed on all the way.

I don't think I would want to be ask to defend this contraption in court.
 

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...85KPSI...

Loading a M98 (even a '93) to the same levels blows the floor plate off, breaks the stock, loses the extractor, blows smoke in all directions BUT backwards. A styrofoam maniquin head behind it has speckles of carbon but no rifle parts in it.

A Rem M700 gets hard to open and blows a primer.
And a Ruger No.1, as I discovered once, just makes you wonder why the bullet hit WAY high (at several hundred meters), as it deposits the freed primer separately from the rest of the case.

85kpsi is not far above where the average shooter will see (or anyway notice) 'pressure signs.' That makes this a ludicrously inadequate design, IMO.

That to one side:
There's generally good technical reason(s) ammunition is let go as surplus.
 
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