when you do not check and balances you hurt hand shoot a gun

[chrislognshot]

[JonM]

That title makes my brain hurt.

[Rusty Brass]

I've been wanting a 50 for a while, almost snagged one a couple of times. Things like this are a large part of my hesitance though. It's a lot of boom with all kinds of ways for things to go wrong.

[freedom]

85,000 psi
ouch...

wait for the money shot of his neck and chest

[boarder2k7]

How gory is the video/what should I skip? I'm very interested but have no desire to add that to my already stressful day tbh

[chrislognshot]

just prove that people only care about getting shots not doing safety before hand. he should checked to see how hot gun was or bullet was before next shot

[infamoussmiley]

Nope... I would be done.

[Axel]

So 55 kpsi is normal, and 85 kpsi makes it explode? Is that a low safety margin? I don't know firearm design

Maybe I'm just biased from watching the video, but a design where you screw the breech block on the back of the barrel gives me the heebie-jeebies. That a lot of faith you're placing on a few threads

[Grendel]

The delta between 85 Kpsi and 55 Kpsi 1.55% which is way larger delta then is typically done in design. Normally 125% over spec is typical in design which 125% of 55Kpsi = 68.75 Kpsi so expecting that rifle to be designed for Max 55 Kpsi in normal operation to withstand 85 Kpsi is an unrealistic expectation. What design tolerances Serbu designed for or any rifle manufacture design for I doubt it is 55% over max design operating pressure.

[Siress]

Grendel, what industry uses % delta instead of 'safety factor'? Anyway, safety factor for pressure vessel burst pressure has always been 4x throughout my engineering career - be it macroline like we use or suspension for a lunar lander. It's 4x. This is why we can get away with using macroline that specifies a maximum operating pressure of 300psi @ room temp; it's actually capable of sustaining 4x300=1200psi before we expect it to burst *in theory*.

[maggot]

So 55 kpsi is normal, and 85 kpsi makes it explode? Is that a low safety margin? I don't know firearm design

Maybe I'm just biased from watching the video, but a design where you screw the breech block on the back of the barrel gives me the heebie-jeebies. That a lot of faith you're placing on a few threads

Exactly what I was thinking. He said the owner of the company making the gun called him. Guessing there's a settlement in progress.

[ReconSWS]

Thanks for the vid! I watched this guy a few times but also the manufacturer and his crew. This 50cal is used by all the gun-youtubers so it seems pretty safe, and what is on display here seems to be an exotic failure as the guy says. Gotta agree with Axel tho that safety margin seems a bit too low but I guess you get what you pay for this is a budget 50 cal.

That being said, I am an armchair engineer on weekends, and it seems like the threads did survive (at least the first 2), meaning the back cap unscrewed itself before blowing off. Definately an over-pressure due to hot rounds (and possibly a squib from using sabot stuff maybe barrel dirty) coupled with long barrel, way too much back pressure it would seem. Definately both parties will have a lot to think about...

[Siress]

Unscrewed itself? During explosive failure? Nah. Not hardly. It just wasn't designed to have every thread engaged.

[matteekay]

Yeah, I suspect the surviving threads were never engaged and the cap bottoms out before reaching them.

[matteekay]

I've been wanting a 50 for a while, almost snagged one a couple of times. Things like this are a large part of my hesitance though. It's a lot of boom with all kinds of ways for things to go wrong.

I've kicked the idea around a few times but the round is overkill for... everything. Calibers like .45-70, .450 Bushy or even .308 are probably more punch than I'd ever need and are relatively cheaper and far safer.

So 55 kpsi is normal, and 85 kpsi makes it explode? Is that a low safety margin? I don't know firearm design

I'm not an engineer (so take it with a huge grain of salt) but I am a competitive shooter and reloader. Pressure curves in ammunition escalate very, very quickly from "well that felt slappy" to "raging inferno of death". For a quick comparison, heavy-hitters like the .500 S&W and even .308 all max out around the 50k mark. More than 1.5 times the pressure, plus the variability in pressure curve / delivery from a sabot round, and you get... well, this.

[Siress]

So, I don't have time to run through the engineering right now but...

I'd wager that the number of rounds this guy has put through the gun played a role. People should be paying close attention to these guns. Once could be a fluke due to the round. A second incident may indicate a design failure. Namely, I think the length of engagement for the threads is far too little; ~4 stripped, minus 1 for lead-in features...=3 turns?! This is probably 4140 steel we're talking about here. I just don't think that's sufficient at 55ksi after several thousand cycles.With as little thread shear area as that'll have with that little engagement, I worry _bet it's above yield...

edit: we need a strike-through feature... I shouldn't make any bets since I'm not super familiar with this alloy. I'm just speculating.

[gabe]

There's a pretty good speculation from another online gun guy that one of the SLAP round sabots got stuck in the barrel possibly due to the muzzle brake catching it. The next round hit the bore obstruction and BOOM. The case of a 50BMG round doesn't have enough capacity to over-load it with the normal mil spec powder they use but of course if these were handloads someone could have substituted a faster burning powder.

[ReconSWS]

Definately the stupid ammo lmao. Like if you can't hit the broad side of a barn cause you ammo is veering off, imagine it just tipping inside the muzzle. These are shitty sabots so super thin pointy tip with some plastic crap keeping it leveled.

[ReconSWS]

I'm sorry but I must re-iterate that I have mystical knowledge of science from ancient scrolls, and it is extremely plausible that gas flow after a squib will induce vortices that could unscrew the cap 2 threads, which would cause it to blow off the rest.

If Mr. Serbu gun nut gun designer REALLY didn't thread that all they way.... then that is some respect lost lmao. I don't believe there is any reason to not thread it all the way.

[ReconSWS]

This is kinda mean but whatever, it's on the website... These 50cals are probably like opiates, the ones that kill the user are the ones that people will want to buy for their potency. Excellent marketing campaign!

'exploded' view - topical

AnSKnWW.jpg


I feel like this type of science question is related to why the cap blew off, as it looks fully threaded from the blown up view : https://www.reddit.com/r/explainlike...tting_it_from/

TLDR : odd pressure changes can create a partial vacuum, making un-threading of a pressurized object easier. On youtube, another guy did "clear silencers" and you can see that there definately is pressure fluctuation from the front to back that yadda yadda yadda I'll stfu

But I'm not gonna jerk my chain anymore I'm no engy

[Axel]

Yeah, I laughed. One ticket to hell, please.

[bored383]

I am wondering if the frame had stretched from use such that it was able to go into battery in an unsafe condition, as one of the contributing factors. I am thinking it was a combo of bad juju that caused the kaboom - sketchy ammo, worn gun, maybe not the best weapon design, operator not paying attention to warning signs

all that said - that guy and his dad had composure in spades. they didnt panic, they reacted quickly and effectively, and they saved his life. and that he is being upfront with presenting it and how, lots of props to them