.50BMG explodes with serious injuries.

Bolt action rifles, lever action, pump action, self loading rifles and other miscellaneous longarms.

Re: .50BMG explodes with serious injuries.

Post by on_one_wheel » 04 May 2021, 9:47 am

InisBineest wrote:While I'm sure those making such assertions about the poor design of the RN-50 are highly qualified gunsmiths and engineers.... May I suggest folks watch an analysis from a well known firearms expert on the incident that they might find interesting/educating.

https://youtu.be/bBNHI1_urWs


A well known expert whos looking a tad wet behind the ears on his YouTube channel "backyard ballistics"

Containing 55,000 psi blast on 4 of 5 turns (less than ⅓ of the threads total diameter) of what looks to be a 1½ to 1¾" thread thats somewhere around 12 TPI is a massive ask let alone asking it to hold additional force from over pressure.
Second to that, the firearms inherent design makes mo allowance for user safety in the event of a catastrophic failure, sending the breach cap and little locating lugs straight at the user ....no thought has been put into its design with regard to engineered failing points.
Definitely a very poorly conceived design.
20210504_091634.jpg
20210504_091634.jpg (57.22 KiB) Viewed 6570 times
Gun control requires concentration and a steady hand
User avatar
on_one_wheel
Colonel
Colonel
 
Posts: 3561
South Australia

Re: .50BMG explodes with serious injuries.

Post by Blackened » 04 May 2021, 10:30 am

on_one_wheel wrote:Pretty nasty looking action, screw on cap with 2 pissy lugs behind it. I guess its a budget 50cal rig?


My first thought as well when I saw it.
User avatar
Blackened
Moderator
 
New South Wales

Re: .50BMG explodes with serious injuries.

Post by Khalild » 04 May 2021, 11:46 am

Blr243 wrote:I tend to agree one wheel. Looks like the sort of thing a backyard jamacain gangster might do with pipe And fittings from mitre ten

demolition ranch owns the same model. bet that wont be making any appearances in his videos anytime soon.
Khalild
Private
Private
 
Posts: 50
New South Wales

Re: .50BMG explodes with serious injuries.

Post by InisBineest » 04 May 2021, 12:17 pm

straightshooter wrote:I watched the video by your 'well known firearms expert' and am somewhat underwhelmed.
It is a fairly good example of motivated reasoning in as much as only facts that support his 'educated guess' were presented and his immediate assertion that the failure was due to a single massive overload.
Now consider this.
The end cap is hand threaded onto the end of the barrel, technically it does not have any preload. It is thus loosely attached to the thread.
Each time a cartridge is fired an impact load is applied to the threaded joint with the possibility of localised thread deformations due to the looseness of the joint.
Eventually a buildup of these deformations can lead to catastrophic failure.
Now try to imagine tearing a thick phone book in half. Once upon a time a popular demonstration of strength. In reality the strongest muscleman was unable to tear the phone book when the book was in it's normal state. The trick was to splay the pages slightly so that pages commenced tearing one at a time and once started offered little further resistance.
That is comparable to what I suspect was the failure mode in this instance.
Somebody babbling their opinions on a youtube video does not automatically promote them to 'expert' status.
Nor am I an expert, but I am happy to sometimes offer my opinion.



Everyone is entitled to an opinion, but on matters like these I'll er towards those who I know to put out reliable analysis'. Your view on it is interesting, and you bring up an interesting point... But I don't know you, or any work you do, nor do I have an engineering background to analyse it myself. Where as I'm reasonably familiar with the content of backyard ballistics, and comfortable with his capacity to put out reliable information based on what he works with.

There are other commentaries on this incident too worth looking at, forgotten weapons did one on "why and how guns explode", and Mark Serbu has his own reply (more sentiment, but a statement that he will be trying to replicate the event... Looking forward to that).

From all information that I can find, and the fact that threaded breech blocks have been used in cannons and artillery for a long time, I'm fairly confident that the rifle failed because of a freak overpressure from bad ammo, that was well above even a proof load. The reality seems to be that although the rifle could have had measures to mitigate the results of such a failure, such an overpressure even in many common firearms with extra safety features could be lethal. My thought would be, how would your average break action 308 fair with a similar event? Don't know, but I doubt it would be good. If anyone wants to lend me a rifle, I'd be happy to load a hot round and see what happens:) (you know, pulling the trigger with a really long piece of string!)


EDIT: I will add one more note, i'm not disputing the fact that it is a cheap rifle, nor that it seems to lack secondary layers of protection in the event of failure. That is a problem, and it was noted in the video I referenced. What I am saying (and this seems to be a point of contention) that by many accounts I can find of people more knowledgeable than I- a threaded breech plug would seem a sensible choice for containing a high pressure event. Flicking through some max SAAMI specifications and looking at the pressures of common round:
223- 55000 psi
308- 62000 psi
30-06- 60190 psi
300 Win mag- 64,000 psi
50bmg- 60,481 psi

These pressures are not dissimilar to one another, and I can find break action rifles (Thompson Contender, CVA Apex, Baikal Single Shots etc) for all but the 50bmg. Now while a break action rifle tends to fail less dangerously (and that is important!), they are each taking some hefty pressures in an action that is considered weaker than bolt actions. I would have thought (in my puny non engineering/gunsmith mind) that a set of well designed threads would be just as, if not more reliable in holding pressure than one or two lugs in a break action, that have been known wear over time and in some cases give (in a less dangerous manner than threads, granted).
Last edited by InisBineest on 04 May 2021, 8:11 pm, edited 1 time in total.
InisBineest
Corporal
Corporal
 
Posts: 257
Victoria

Re: .50BMG explodes with serious injuries.

Post by Larry » 04 May 2021, 2:10 pm

Over pressure vents either built into this rifle that exploded or your common modern bolt action already with over-pressure vents will only work in certain circumstances or will not work under certain circumstances. The determining factor is how much pressure is the overload and how quickly can it vent to a low pressure. so the path it must take is important and any restrictions it may encounter on the way slowing the vent for example. In bolt guns it usually relies on the firing pin to be cleared away from the bolt firing pin hole.
Larry
Staff Sergeant
Staff Sergeant
 
Posts: 775
-

Re: .50BMG explodes with serious injuries.

Post by on_one_wheel » 05 May 2021, 9:59 am

InisBineest wrote: I would have thought (in my puny non engineering/gunsmith mind) that a set of well designed threads would be just as, if not more reliable in holding pressure than one or two lugs in a break action, that have been known wear over time and in some cases give (in a less dangerous manner than threads, granted).


Threads can hold more pressure than a couple of bolt lugs PROVIDED they are of sufficient size, have enough thread engagement, enough thread length and as mentioned enough thread preload.
The thread on that firearm had poor engagement which can be seen by how easily it was screwed on, very little thread length of only about 4 or 5 threads which is evident in the screen shot earlier in this thread, and the cap is not shouldered (zero preload)
Its a recipe for disaster.
Gun control requires concentration and a steady hand
User avatar
on_one_wheel
Colonel
Colonel
 
Posts: 3561
South Australia

Re: .50BMG explodes with serious injuries.

Post by Bill » 05 May 2021, 1:15 pm

I was thinking about the projectile of the slap round, looks like there would be alot of projectile in the lands maybe even Jammed. When fired the torque from engaging the rifling would be thrust back on upon the screw on cap in a rotational force. Did I miss something is there a grub screw of some sort of lock to prevent the cap from unscrewing ??

either way when a 50 BMG cost only $1100 US you gotta ask yourself did they cut some corners ?? was the screw cap and threads appropriately heat treated ??
When a guy is digging his own grave, you don’t fight him for the shovel.

Success leaves clues, Fools follow failure !

20 Hornet, 218 Bee, 222 Rem, 256 WM, 6mm ARC, 6.5 Grendel, 6.5x55 Scan, 270 Win, 357 Mag, 358 Win, 9.3x62, 500 A Square
User avatar
Bill
Warrant Officer C1
Warrant Officer C1
 
Posts: 1253
New South Wales

Re: .50BMG explodes with serious injuries.

Post by linkoln » 05 May 2021, 1:28 pm

Would you risk your life to a couple of tiny threads. Maybe if it was a .22 I wouldn't mind the only thing being between me and an explosion was a cap held on by a thread but 50BMG is in a league of its own.
And from what I understand these guns were made by an amateur who got taken on by a big company to make these guns.
linkoln
Lance Corporal
Lance Corporal
 
Posts: 166
-

Re: .50BMG explodes with serious injuries.

Post by InisBineest » 05 May 2021, 2:08 pm

https://youtu.be/p7LjeJNewBs

Same guy, more discussion/information on threads. Interesting to watch.
InisBineest
Corporal
Corporal
 
Posts: 257
Victoria

Re: .50BMG explodes with serious injuries.

Post by Insert random name » 05 May 2021, 2:46 pm

TiborasaurusRex thinks it is the sabot part of the round leaving residue in the muzzle brake, he has manuals that talk about the danger of those rounds in muzzle brakes not designed for them
https://youtu.be/ardw09S7GfE?t=1
Insert random name
Recruit
Recruit
 
Posts: 34
Queensland

Re: .50BMG explodes with serious injuries.

Post by disco stu » 05 May 2021, 4:30 pm

What's the comparison between these cap threads and those holding a barrel in the action?
disco stu
Sergeant
Sergeant
 
Posts: 526
New South Wales

Re: .50BMG explodes with serious injuries.

Post by bladeracer » 05 May 2021, 6:20 pm

Insert random name wrote:TiborasaurusRex thinks it is the sabot part of the round leaving residue in the muzzle brake, he has manuals that talk about the danger of those rounds in muzzle brakes not designed for them
https://youtu.be/ardw09S7GfE?t=1


If the muzzle were obstructed, that's where it would rupture, not at the breech.
Practice Strict Gun Control - Precision Counts!
User avatar
bladeracer
Field Marshal
Field Marshal
 
Posts: 12655
Victoria

Re: .50BMG explodes with serious injuries.

Post by disco stu » 05 May 2021, 6:45 pm

I would think muzzle threads would be much weaker than what is at the rear. Still, combined with other possible things posited it could have contributed.

Was interested to hear gun Jesus (forgotten his name) talk about aging powder being a possibility. I was only reading about various powder types few days before this vid was posted, and took note of some powder becoming more unstable and somewhat explosive as it ages. I quietly wondered about that in this case.
disco stu
Sergeant
Sergeant
 
Posts: 526
New South Wales

Re: .50BMG explodes with serious injuries.

Post by wanneroo » 06 May 2021, 12:34 am

Yeah the thing is 50 BMG is a whole different ball game with the force involved. Not to be messed around with in any way.

Decades ago when my dad was a military doctor, there was a soldier that popped the top cover off a hot M2 machine gun and had his body/face close to it and a round cooked off and exploded. The shrapnel killed him dead and he was pretty much dead by the time my dad attempted to treat him. I've heard of similar injuries.
wanneroo
Warrant Officer C1
Warrant Officer C1
 
Posts: 1412
United States of America

Re: .50BMG explodes with serious injuries.

Post by straightshooter » 06 May 2021, 8:27 am

disco stu wrote:What's the comparison between these cap threads and those holding a barrel in the action?

The threaded joint of a barrel into an action is usually quite a close fit and has considerable preload, that is, it is done up so tight as to be considered immovable.
The end result is that the joint is not weakened by being subjected to repeated shocks from firing.
This is also assisted by there being an approximate balance in the substantial mass of the barrel with the substantial mass of the receiver and stock assembly.
"Anything is possible if you don't know what you are talking about."
"There is no expedient to which a man will not resort to avoid the real labor of thinking." Sir Joshua Reynolds
straightshooter
Warrant Officer C1
Warrant Officer C1
 
Posts: 1263
New South Wales

Re: .50BMG explodes with serious injuries.

Post by Blr243 » 06 May 2021, 4:34 pm

Buggered if I know how those smiths manage to screw and u n screw barrrels without surface marks
Blr243
Brigadier
Brigadier
 
Posts: 4479
Queensland

Re: .50BMG explodes with serious injuries.

Post by disco stu » 06 May 2021, 4:54 pm

straightshooter wrote:
disco stu wrote:What's the comparison between these cap threads and those holding a barrel in the action?

The threaded joint of a barrel into an action is usually quite a close fit and has considerable preload, that is, it is done up so tight as to be considered immovable.
The end result is that the joint is not weakened by being subjected to repeated shocks from firing.
This is also assisted by there being an approximate balance in the substantial mass of the barrel with the substantial mass of the receiver and stock assembly.


Cheers. Yes, good points on the inertia of those parts vs the cap and the pre load, of which the cap really has none. What are typical thread dimensions of barrel threads?
disco stu
Sergeant
Sergeant
 
Posts: 526
New South Wales

Re: .50BMG explodes with serious injuries.

Post by bladeracer » 06 May 2021, 5:45 pm

disco stu wrote:
straightshooter wrote:
disco stu wrote:What's the comparison between these cap threads and those holding a barrel in the action?

The threaded joint of a barrel into an action is usually quite a close fit and has considerable preload, that is, it is done up so tight as to be considered immovable.
The end result is that the joint is not weakened by being subjected to repeated shocks from firing.
This is also assisted by there being an approximate balance in the substantial mass of the barrel with the substantial mass of the receiver and stock assembly.


Cheers. Yes, good points on the inertia of those parts vs the cap and the pre load, of which the cap really has none. What are typical thread dimensions of barrel threads?


The cap is preloaded against the shoulder of the barrel, the face of the cap is hard against the face of the barrel, and the inside of the rear of the cap is hard against the face of the chamber - that is how it is head-spaced. It's only hand-tight, but it is still in tight contact with the threads. If it were not fully tightened, the action can't be closed due to the pair of safety lugs behind the cap.

Barrel threads vary greatly. Frank DeHaas' book, Bolt Action Rifles has a good selection of barrel thread diagrams for older rifles. For most centrefire bolt-actions you're generally looking at roughly 22mm to 25mm major diameter, about 16mm to19mm of thread (barrels that use a lock nut have a lot longer thread), at ten to sixteen threads per inch. Some barrels are not threaded at all, they fit into the receiver and are held in place by a nut around the receiver, or some other attachment. Some barrels are simply press-fitted into the receiver with no other locking system - the Ruger Americans for example.

A few examples:
Sako L-46 is .855" major diameter, .845" long, 16TPI.
Pattern 14 Enfield is 1.125" major diameter, 1.084" minor diameter, .720" long, 10TPI square thread.
Springfield M1903/A3/A4 is 1.040" major diameter, .990" minor diameter, .734" long, 10TPI square thread.
Arisaka Type 99 7.7mm is 1.050" major diameter, .700" long, 17TPI.
No.1/No.4/No.5 Rifle is .997" major diameter, .687" long, 14TPI.
M98 Mauser is 1.100" major diameter, .625" long, 12TPI.

I don't have numbers for modern firearms, or for any .50BMG rifles, but they might be available online.
Practice Strict Gun Control - Precision Counts!
User avatar
bladeracer
Field Marshal
Field Marshal
 
Posts: 12655
Victoria

Re: .50BMG explodes with serious injuries.

Post by disco stu » 06 May 2021, 8:08 pm

Thanks blade racer. Those threads are much coarser than I pictured, or in some at least.

What I'm thinking as pre load is torqued up appropriately so that all potential slack between threads is taken out, which wouldn't happen with hand tight on normal threads. I guess it depends on the thread used on that cap and tolerances. Not that I'm saying I think it's a cause or that I think it isn't, just that it's an interesting thought
disco stu
Sergeant
Sergeant
 
Posts: 526
New South Wales

Re: .50BMG explodes with serious injuries.

Post by pomemax » 07 May 2021, 12:45 am

look up project "eldest son " used by CIA in Vietnam they done it to 7.62 and 12.7 rounds and the guy in the video said they were ex service rounds just a thought
pomemax
Warrant Officer C2
Warrant Officer C2
 
Posts: 1165
New South Wales

Re: .50BMG explodes with serious injuries.

Post by Ed9362 » 08 May 2021, 5:47 pm

i haven't posted for a while but i just wanted to point out that 85000 PSI is a massive overpressure.
I would have though you could expect a catastrophic failure in any rifle with such a large overpressure.
i don't really see how the threaded end cap is relative to the failure of the firearm considering any gun would have failed under similar conditions.
i understand that a different gun may have failed differently resulting in less injuries to the shooter, but either was you are setting of a bomb.
Ed9362
Lance Corporal
Lance Corporal
 
Posts: 124
Victoria

Re: .50BMG explodes with serious injuries.

Post by bladeracer » 08 May 2021, 6:19 pm

Ed9362 wrote:i haven't posted for a while but i just wanted to point out that 85000 PSI is a massive overpressure.
I would have though you could expect a catastrophic failure in any rifle with such a large overpressure.
i don't really see how the threaded end cap is relative to the failure of the firearm considering any gun would have failed under similar conditions.
i understand that a different gun may have failed differently resulting in less injuries to the shooter, but either was you are setting of a bomb.


Exactly, I doubt the M2 Machinegun would've tolerated that specific cartridge.
Practice Strict Gun Control - Precision Counts!
User avatar
bladeracer
Field Marshal
Field Marshal
 
Posts: 12655
Victoria

Re: .50BMG explodes with serious injuries.

Post by disco stu » 08 May 2021, 9:47 pm

I'm intrigued if there was any ammunition left over and if anyone is looking at the powder in those. Might shed some light into the cause and tell if there was old powder, incorrect type etc.

That protect oldest son is interesting reading. I particularly like the part where they made fake documents from higher command indicating they knew of the problem
disco stu
Sergeant
Sergeant
 
Posts: 526
New South Wales

Re: .50BMG explodes with serious injuries.

Post by bladeracer » 20 Feb 2022, 1:38 pm

Scott's latest attempt to blow another RN50.
https://www.youtube.com/watch?v=hsw70VfSFFw

This is after firing another of the dodgy SLAP round, the case head is imprinted into the breech face!
Attachments
Scotts RN50.jpg
Scotts RN50.jpg (20.2 KiB) Viewed 4068 times
Practice Strict Gun Control - Precision Counts!
User avatar
bladeracer
Field Marshal
Field Marshal
 
Posts: 12655
Victoria

Re: .50BMG explodes with serious injuries.

Post by boingk » 20 Feb 2022, 7:04 pm

Good watching, and interesting result. Won't spoil it here but its worth a watch, even if you just go to near the end.

All the experts commenting on threads being insufficient - you realise threads are how are rifles are put together, right?

And that for containment purposes most thread strength (roughly 80%) is in the first 4 rows? Very little gain is made by going to 5 or 6 threads over four, and anything over that is virtually useless.

This comes down to a massive overpressure situation. I wouldn't want to be behind the butt of any firearm where there is a potentially destructive overpressure. There's all sorts of risks, stories and anecdotes. I;ve seen pictures of rifle bolts leaving rearward, revolver top straps and cylinders breaking, containment lugs sheared... all nasty sorts of injuries and quite usually causing savage injuries to the hands, limbs and face of the user at the time.

Would I trust a threaded cap? I would, and so do you, every time we fire a rifle. Would I ever want to go into an overpressure situation? JH Christ, no!

To quote a member here 'I see no utility in pushing a catridge to the limits. Its fatiguing on both shooter and rifle, and ultimately dangerous. Just go to another caliber.'

- boingk
Nil
boingk
Sergeant
Sergeant
 
Posts: 682
Other

Re: .50BMG explodes with serious injuries.

Post by bladeracer » 20 Feb 2022, 7:47 pm

In the US it appears to be fairly common practice to buy bulk surplus ammo for bugger all, pull them apart for the brass and bullets, and sell the powder cheap. People are always asking for load data "for this powder I saved from some 5.56 NATO ammo".

My guess is somebody unscrupulous bought a bunch of salvaged powder for nothing, found some brass, and fabricated some dummy saboted bullets - maybe they even found a source of genuine penetrators and sabots and saw a way to make some good money. It would be very easy to 3D-print the sabot to replicate an original. It's probably very easy to turn replicas of the 7.62mm penetrator out of brass or steel and paint them to match. Filled the brass with a mixture of old powders from different sources, and seated the bullets on top. When your profit margin is something like US$90 per round people will make the effort. That would explain why some fire just fine, some lock the rifle up, and some explode.

This was certainly not a result of any deficiencies in the design of the rifle.

"Cartridge, caliber .50, saboted light armor penetrator (SLAP), M903
This cartridge has a 355 – 360 gr (23.00 – 23.33 g) heavy metal (tungsten) penetrator that is sabot-launched at a muzzle velocity of 4,000 ft/s (1,219 m/s). The 0.50 in (12.7 mm) diameter sabot is designed to separate after leaving the muzzle, releasing the 0.30 (7.62 mm) penetrator. It is injection molded of special high strength plastic and is reinforced with an aluminum insert in the base section. The cartridge is identified by an amber sabot (Ultem 1000). For use only in the M2 series of machine guns. This round can penetrate 0.75in (19 mm) of steel armor at 1,500 yards (1,400 m).[12]"
SLAP 1-15.jpg
SLAP 1-15.jpg (144.27 KiB) Viewed 4011 times
Practice Strict Gun Control - Precision Counts!
User avatar
bladeracer
Field Marshal
Field Marshal
 
Posts: 12655
Victoria

Re: .50BMG explodes with serious injuries.

Post by InisBineest » 21 Feb 2022, 6:44 am

After the last video, I would suggest that it puts to bed the idea of it being an inherit fault of the rifle.
It is a cheap 50cal, and cheap often equals poor quality.
But this wasn't a cheap 50 cal on equal footing to other semi automatics. It is basically a rifle at its simplest. Any simpler and you have a matchlock. I'd still be happy to own an RN-50 (if only I could afford to shoot it in Aus!) But I would be inclined to load my own ammo, as I am for all my rifles (less the .22 that is:).
That way any blow up is my own responsibility. I'm generally not one to trust milsurp ammo.
InisBineest
Corporal
Corporal
 
Posts: 257
Victoria

Re: .50BMG explodes with serious injuries.

Post by on_one_wheel » 21 Feb 2022, 10:27 pm

My opinion of the plug thread length engagement, shouldering and preloading hasn't changed.
That's not a great place to have the point of failure, it's just plain deadly.
I personally think that no thought has been put into engineering the rifle in such a way that in the event of failure the user is kept from almost certain death.
Having the breach plug and lugs fired at the user isn't ideal. Having a destroyed shoulder and a barrel sent down range would be a better option.
If I were to redesign that rifle, I'd be making sure that the weakest point was a point on the chamber area of the barrel, milled down to a flat on the top, allowing the chamber to to explode upwards sending the energy and shrapnel in a safer and more controlled direction. I'd definitely be making the breach plug thread and lugs a point of no failure.
Even a groove machined on the od just behind where the shoulder would be sitting inside, engineered blow the barrel forward.
Gun control requires concentration and a steady hand
User avatar
on_one_wheel
Colonel
Colonel
 
Posts: 3561
South Australia

Re: .50BMG explodes with serious injuries.

Post by cz515 » 21 Feb 2022, 10:46 pm

Pay peanuts get monkeys.

I think the design is bad. The cartridge is put in and then back ends screwed in, ofcourse people are impatient so the designers probably thought having less threads would be good enough. In this case likely not
When good men and women can’t speak the truth, when facts are inconvenient, when integrity and character no longer matter, when ego and self-preservation are more important than national security — then there is nothing left to stop the triumph of evil
User avatar
cz515
Warrant Officer C2
Warrant Officer C2
 
Posts: 1032
Victoria

Re: .50BMG explodes with serious injuries.

Post by bladeracer » 21 Feb 2022, 10:55 pm

cz515 wrote:Pay peanuts get monkeys.

I think the design is bad. The cartridge is put in and then back ends screwed in, ofcourse people are impatient so the designers probably thought having less threads would be good enough. In this case likely not


It wouldn't matter how many threads there were, it still would've blown with that charge. If the threads had held it would've blown the cap apart. It would not have contained the pressure.
Practice Strict Gun Control - Precision Counts!
User avatar
bladeracer
Field Marshal
Field Marshal
 
Posts: 12655
Victoria

PreviousNext

Back to top
 
Return to Centerfire rifles