Author Topic: Kentucky Ballistics - My 50 Cal Exploded  (Read 6652 times)

Jim147

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #25 on: May 03, 2021, 05:08:10 PM »
A sabot down a brake gives me the same not fuzzy feeling that a gas check sent down a canned rifle does.
Sometimes we carry more weight then we owe.
And sometimes goes on and on and on.

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French G.

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #26 on: May 04, 2021, 12:13:18 AM »
Feel like a Ross rifle thing. Great rifle, may kill ya if you don't do it just so. Make a design with failsafes and actual bolt lugs. Single shot bolt AR uppers are not astronomical.
AKA Navy Joe   

I'm so contrarian that I didn't respond to the thread.

dogmush

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #27 on: May 04, 2021, 02:59:33 AM »
Mark responds (sorta).

https://www.youtube.com/watch?v=5AY6iEVhJE8&t=340s


I think if you are designing firearms you really need to design the failure mode into it.  You can make the strongest gun ever, and some dingus will fill it with C4 and touch it off.  Failure mode design is as important, if not more, then the "normal use" engineering.

K Frame

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #28 on: May 04, 2021, 10:37:19 AM »
The more I'm hearing/reading/seeing about this, the more I think it's not an issue with the rifle at all.

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makattak

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #29 on: May 04, 2021, 10:54:15 AM »
I had to stop watching once he started talking about what he did to stop the bleeding. I was actually getting sick to my stomach when he talked about what he had to do.

He's amazingly blessed to still be breathing.
I wish the Ring had never come to me. I wish none of this had happened.

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Brad Johnson

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #30 on: May 04, 2021, 11:05:10 AM »
The more I'm hearing/reading/seeing about this, the more I think it's not an issue with the rifle at all.

Same. Everything points to a massive overpressure, something far beyond any safety margins that could be reasonably engineered into the rifle.

Brad
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MechAg94

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #31 on: May 04, 2021, 11:33:07 AM »
The only fault with the rifle is in engineering the failure point so it does not endanger the shooter.  That doesn't mean they are at fault, it just means the owners should be aware of that and take precautions with unknown ammo.
“It is much more important to kill bad bills than to pass good ones.”  ― Calvin Coolidge

K Frame

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #32 on: May 04, 2021, 12:54:39 PM »
"The only fault with the rifle is in engineering the failure point so it does not endanger the shooter."

Realistically an impossibility in most, if not all, cases.

But, in this case, and as others have pointed out, I think the choice of thread type on the breech cap is a bit on the suspect side.
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MechAg94

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #33 on: May 04, 2021, 03:55:15 PM »
I would be curious if changing the thread type alone would make enough of a difference. 
“It is much more important to kill bad bills than to pass good ones.”  ― Calvin Coolidge

dogmush

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #34 on: May 05, 2021, 06:27:30 AM »
Some interesting and more technical takes on the rifle design and failure mode here:

https://www.youtube.com/watch?v=bBNHI1_urWs

https://www.youtube.com/watch?v=p7LjeJNewBs&t=314s

One thing that caught my ear in the first video is the huge increase in bolt thrust for any given chamber pressure in this design if the case ruptures and gas gets behind the case head.  I hadn't thought of that, and .50 brass is pretty tough, but the difference in forces between 80,000 PSI on .75 sqin, and 80,000 PSI on 1.5 sqin is pretty large, and this breech design is particularly susceptible to that, if high pressure gas gets between the cap and the barrel.

I reiterate my opinion that this thing needs vents.

K Frame

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #35 on: May 05, 2021, 06:53:31 AM »
OK, I was apparently wrong about the ability and usefulness of venting the cap.

Very interesting.
Carbon Monoxide, sucking the life out of idiots, 'tards, and fools since man tamed fire.

K Frame

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #36 on: May 05, 2021, 09:34:41 AM »
Come to think of it... has the case been found? Has anyone examined it for failure mode?
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dogmush

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #37 on: May 05, 2021, 10:12:30 AM »
Come to think of it... has the case been found? Has anyone examined it for failure mode?

I thought Scott said he was sending all the pieces back to Serbu.  I assume that would include any pieces of the case he could find.

dogmush

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #38 on: May 05, 2021, 10:18:17 AM »
Also, In the ultimate YouTuber "merch links in bio" move, He's already got "Just put a thumb in it" T-shirts for sale.

https://bunkerbranding.com/pages/kentucky-ballistics

 :lol: :lol:

WLJ

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #39 on: May 06, 2021, 05:50:12 PM »
In case some weren't aware Ian of Forgotten Weapons had an "incident" himself although I don't recall if it was ever stated exactly what it was that occurred  beyond it was an out of battery. IIRC he still carries metal in his chest from it to this day.

Dangerous Things are Dangerous: The Importance of Medical Training
https://www.youtube.com/watch?v=-FhFw86Xk7o




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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #40 on: May 08, 2021, 10:42:04 PM »
Also, In the ultimate YouTuber "merch links in bio" move, He's already got "Just put a thumb in it" T-shirts for sale.

https://bunkerbranding.com/pages/kentucky-ballistics

 :lol: :lol:
Can't blame him there, I imagine he's gonna have some pretty impressive medical bills before long - on top of all the days of live-saving care, he had reconstructive surgery to his face.

In case some weren't aware Ian of Forgotten Weapons had an "incident" himself although I don't recall if it was ever stated exactly what it was that occurred  beyond it was an out of battery. IIRC he still carries metal in his chest from it to this day.

Dangerous Things are Dangerous: The Importance of Medical Training
https://www.youtube.com/watch?v=-FhFw86Xk7o





This is why I have 3 or 4 medical kits scattered everywhere - in the house, in the car, in the mall ninja vest, in the backpack for hunting/shooting range/hiking stuff. They don't have the most tactical tourniquet on the market, but they're inexpensive enough I could buy them and put them everywhere.

Hawkmoon

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #41 on: May 08, 2021, 11:07:54 PM »
Some interesting and more technical takes on the rifle design and failure mode here:

https://www.youtube.com/watch?v=bBNHI1_urWs


First video -- when he got to the discussion of the number of threads engaged (around the 03:50 mark) I stopped listening. I just spent 7 years as an inspection supervisor on a major construction project. The number of threads engaged is a MAJOR concern, and to claim that even if there were 50 threads engaged only the first four would have taken 80% of the load is so totally off-the-wall that I'm not going to even finish watching the video.
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dogmush

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #42 on: May 09, 2021, 12:56:16 AM »
My machinist books teach a couple rules of thumb on threads.  One says that the strength of the bolt is reached around 3 threads (assuming same material).  The other says to design for 1-1.5x the diameter of the fastener for thread engagement.
Both say some version of there's no point in making a bunch of extra threads because the joint doesn't get that much stronger after the optimum thread engagement.

[shrug]

RoadKingLarry

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #43 on: May 09, 2021, 01:09:36 AM »
How many threads are engaged in a typical large (>3/4") nut and bolt? At what point does it achieve optimal/max strenght?
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Hawkmoon

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #44 on: May 09, 2021, 01:47:16 AM »
My machinist books teach a couple rules of thumb on threads.  One says that the strength of the bolt is reached around 3 threads (assuming same material).  The other says to design for 1-1.5x the diameter of the fastener for thread engagement.
Both say some version of there's no point in making a bunch of extra threads because the joint doesn't get that much stronger after the optimum thread engagement.

[shrug]

Sure -- but what's the diameter of that breech cap? It had what, maybe four or five threads engaged?

I know in automotive suspension work, the commercial truck spring place where I get U-bolts for my Jeep leaf springs supplies the U-bolts with double-height nuts -- twice the height (and number of threads, obviously) of a standard hardware store nut of the same diameter and thread pitch. I assume they do that for a reason.
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dogmush

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #45 on: May 09, 2021, 02:44:42 AM »
How many threads are engaged in a typical large (>3/4") nut and bolt? At what point does it achieve optimal/max strenght?

According to Fastenal, a standard 3/4-10 NC nut is .656" thick.  so call it 6 full threads and a little extra.  (I note that's a little short of the 1-1.5x diameter my book says for making threads, but again {shrug} I'm not an expert by any means.)  As far as max strength, I assume that each added thread adds some strength, but the optimal thread engagement is where diminishing returns really take over.  Optimal strength of a threaded joint is probably usage specific.

Sure -- but what's the diameter of that breech cap? It had what, maybe four or five threads engaged?

I know in automotive suspension work, the commercial truck spring place where I get U-bolts for my Jeep leaf springs supplies the U-bolts with double-height nuts -- twice the height (and number of threads, obviously) of a standard hardware store nut of the same diameter and thread pitch. I assume they do that for a reason.

I think we've (the internet) have been saying it's about an 1.5 diameter, but I don't know how the fact that it's a donut plays into that.  It's not like a solid 1.5" bolt.

On the leaf spring thing I just put a lift on my F150, and it too has tall nuts for the leaf spring u-bolts.  Tall, grade 8 at that.  I'd be interested in why that got speced actually, I suspect that the pull on those bolts is really high, and uneven, trying to resist lateral movement of the axle when off camber or cornering. (the leaf spring would try and tilt on the axle with a lateral load, and one half of the bolt would be in compression, while the other half is in tension)  That may have some crazy loads, but the math is beyond me.

To be clear, I'm not arguing the RN-50 has "enough" threads, or that 4 is indeed the "right" number of threads like the video said.  I'm more trying to learn more through the discussion, and the extra research the discussion sends me on. 

For another data point Howitzers still use interrupted threads to close cannon breeches.  Here is the open breech of an M109 155m Paladin:


Even halving the number because of the interruptions, that's more than 4 threads.

Hawkmoon

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #46 on: May 09, 2021, 09:50:18 AM »

For another data point Howitzers still use interrupted threads to close cannon breeches.  Here is the open breech of an M109 155m Paladin:
...
Even halving the number because of the interruptions, that's more than 4 threads.

And those don't look like standard 60-degree machine screw threads -- those look more like Acme threads.
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K Frame

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #47 on: May 10, 2021, 06:59:07 AM »
"Even halving the number because of the interruptions, that's more than 4 threads."

I'd think you'd want/need additional thread engagement on an interrupted screw style breech because you're concentrating one hell of a lot more force on the threads that are there...

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dogmush

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #48 on: May 10, 2021, 09:46:56 AM »
I would have spitballed that 16 half threads and 8 full threads should have similar strengths.

Hawkmoon

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Re: Kentucky Ballistics - My 50 Cal Exploded
« Reply #49 on: May 10, 2021, 10:48:41 AM »
I would have spitballed that 16 half threads and 8 full threads should have similar strengths.

I would have said the same thing.

Quote from my first year structural engineering professor (best read with a heavy Scottish accent): "Stress goes where there's material there to resist it."
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