In reply to Stampie :
As cousin Eddie said. "Bingo"
In reply to Stampie :
As cousin Eddie said. "Bingo"
In reply to Fueled by Caffeine :
It's only the prototype he was showing off in the video that isn't heat treated. All production models are.
In reply to Stampie:
He's quirky for sure, probably abrasive to some. The RN-50 is the cheapest option to buy a .50 BMG it's an evolution of that goofy Royal Nonesuch's home made, plumbing pipe, slam fire guns, literally assembled from hardware store parts.
The US and Jordanians thought his Super Shorty shot guns (AOW) were good enough to add to their military arsenals, but his company is just him a couple guys and his daughter, real small, low production. Ian from Forgotten Weapons said it best in the BFG-50A episode, trying to figure out what the intended market for it was, military, target shooters? Mark Serbu laughed and said, "it was intended for Mark Serbu."
Mezzanine said:Kendall_Jones said:He kept saying there was no way to know that that load was "spicy" - actually you can weigh the rounds. A double load will weigh more. You have to use a gram scale of course. I shoot older guns with surplus rounds and always used to do a sanity check when buying imported rounds. I find the swiss make the most repeatable rounds. ;)
When I first started reloading, I thought this would be true. I tried weighing rounds to confirm the powder charge in cases where I wasn't 100% sure...turns out it's not really possible in smaller calibers due to the variation in brass casing weights. There's a huge inconsistency from one brass manufacturer, and even a lesser inconsistency in brass from the same company.
I'm vaguely remembering something about some types of powder having their pressure controlled by powder shape - large balls, small balls, cylinders, etc - and the surface area affects burn rate.
Upshot, is old ammo that has been handled and moved around a lot, maybe even sent through a tumbler, gets the granules broken up, so there's more surface area, and now you have an overcharged cartridge...
Having been standing near by at a USPSA match when one of my friends blew up his .357 with an accidental double charge I can so relate. The top strap of the revolver, with an Aimpoint scope mounted, was propelled 5 feet into the air. The Cylinder blew into three pieces. Once piece embedded itself into a cinder block wall next to me at about neck level. Missed me by about a foot.
I was standing at least 10 feet behind and 25 feet laterally from him. No one, thankfully, was injured, other than my friend's pride for the double charge. If that chunk of cylinder had hit me in the neck I would have been killed.
Pete. (l33t FS) said:Mezzanine said:Kendall_Jones said:He kept saying there was no way to know that that load was "spicy" - actually you can weigh the rounds. A double load will weigh more. You have to use a gram scale of course. I shoot older guns with surplus rounds and always used to do a sanity check when buying imported rounds. I find the swiss make the most repeatable rounds. ;)
When I first started reloading, I thought this would be true. I tried weighing rounds to confirm the powder charge in cases where I wasn't 100% sure...turns out it's not really possible in smaller calibers due to the variation in brass casing weights. There's a huge inconsistency from one brass manufacturer, and even a lesser inconsistency in brass from the same company.
I'm vaguely remembering something about some types of powder having their pressure controlled by powder shape - large balls, small balls, cylinders, etc - and the surface area affects burn rate.
Upshot, is old ammo that has been handled and moved around a lot, maybe even sent through a tumbler, gets the granules broken up, so there's more surface area, and now you have an overcharged cartridge...
Correct.
I worked in large caliber tank rounds for a couple years. There are also coatings and other things that affect burn rate. I know that medium caliber stuff uses those tricks, but I'm not sure if the small caliber stuff has enough room to use those tricks.
Fueled by Caffeine said:I'm gonna arm chair engineer this a bit. I've always been taught that to get full strength out of a threaded joint you need to have the thread engagement equal to the diameter of the bolt.
Actually, while a full diameter (or 1 1/2 diameters) is good practice for a number of reasons, the loads are pretty much all taken up in the first three threads, and even that assumes a softer "nut" than the bolt. The rules change a little for threading steel into aluminum, or plastic, etc., but that is not the case here. Keep in mind, for any given grade of bolt, the bolt still often fails before the nut, even though nuts are generally much shorter than a full diameter deep.
The reality is that it is trivially simple to blow up a gun by screwing up the load; you don't even have to try. While the gun design in the video is very simple, and looks odd, the video also shows odd things going on with the ammo even before the gun blew up. Surplus ammo can be fun. Surplus ammo can be cheap. I have shot a lot of surplus ammo. Usually the effects of age show up in decreased reliability (actual firing) and an increased chance of hangfires, or even embrittlement of the brass. The truth is, the only thing you can be certain about is that the owning military, despite limited training budgets, didn't even want to use the ammo for training purposes, so they got rid of it.
matthewmcl (Forum Supporter) said:...the loads are pretty much all taken up in the first three threads...
Your "pretty much all" is barely more than 70%... While it's certainly 'most', I don't consider that particularly close to 'all'.
Even when there is proper thread engagement, the first thread in a fine thread sees nearly 30% more of the mean shear stress than the first thread in a coarse thread. Thus threads shearing off is a considerably more likely primary failure mode, occurring at a lower threshold, for fine threads than coarse threads. This is typically alleviated by engaging more threads when fine threads are selected.
The limited number of apparent engaged threads on the breech cap in question is compounded by also being fine thread.
In reply to Driven5 :
I think the other issue is the impulse/shock loading nature of this joint. We're not talking a nicely torqued joint with a constant load. I'm not smart enough t comment anymore But I agree with you.
In the end. I'm skeptical of the design. All other designs I've seen with removable breach plugs use the barrel as the female and the breech plug as the mail. Think later 19th century cannon. I wouldn't fire this thing.
Someone else on another forum pointed out probably the leading cause -- I was gonna say "smoking gun" but I have too much good taste to stoop that low-- that I hadn't thought of. But SLAP rounds are sabot rounds. The sabot come off at the muzzle and the round goes its merry way downrange. This makes sabot rounds completely incompatible with muzzle-braked barrels, which this Serbu's is (well, was). An excellent way to obstruct the barrel, this is...
85K always seems low for a pressure for that sort of thread and how deep it took off the threads. Armchair gun guy here says someone reloaded that round or made it at home to sell as a slap and used half rifle powder or full power pistol powder and bult a bomb.
So he has no record of reasonably determining or testing the failure strength and failure mode of his rifle design(s) prior to manufacturing and selling (over 1000 of) them, relies after-the-fact on what he himself wasn't knowledgeable enough to immediately identify as a "crap in = crap out" rudimentary analysis from some random/supposed 'Mechanical Engineer Buddy' in half way around the world who completely fails to take into account any amount of unequal thread load distribution, let alone rate of (impact) load application or potential fatigue life effects, publicly presents this faulty analysis in his defense as being in any way reputable or definitive, and indirectly claims that a gun only 'needs' to be as strong as would plastically deform it from the pressure of a single normal/typical round... Yeah, that latest video did nothing to improve my opinion. While I'm sure his faithful followers will gobble up his quasi-technical analysis and explanation without question, regurgitating them it everywhere they can, in my humble opinion this is all just more fodder for a good lawyer armed with a PE.
That's not to say the ammo isn't primarily at fault in this particular instance, and that this very well might have failed other better designed rifles as well, but it has also highlighted some apparent substantial shortcomings in the design that he is responsible (and ultimately liable) for.
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