Why did my gun blow apart?

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Derringeer

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I made a gun that blew apart today. It was made as a 3-shot muzzleloader, with three individual barrels lined up at top of eachother (similar to the cartridges i described in the ”how strong are cartridges” thread I made a couple of days ago). As a source of ignition I used electrical igniters, that were inserted into a hole in the breech of each barrel.

The barrels didn’t blew up, but the ”receiver” blow apart. I think the design of the receiver is best understood by looking at it, so here’s some pictures of the damaged receiver:

https://imgur.com/fQhFc7V

https://imgur.com/1nv5wM5

So, the wooden grip were inserted into the steel part (that holds the barrels in place let’s call it the receiver-chamber) and fixed together with JB-weld. The force of the recoil pulls the barrel that’s firing towards the breechface of the receiver, which with some blutak or similar sealment prevents any gas leaking out of the ”touch hole” (let’s call it the breech-hole) at the breech of the barrel, where the electrical igniter is inserted.

Since I didn’t secured the receiver-chamber, but secured the grip in a vise it shouldn’t be any force of recoil pulling the assembly apart. But the barrels were somewhat secured to the receiver-chamber with some electrical tape just to hold them in place.

What happen was that it blew apart and the fired barrel flew forward, so I wounder if it blow apart because of force from the breech-hole and not the recoil? I think that the pressure from the gas at the breech-hole forced the breech face (that’s part of the grip) to blow apart and at the same time forcing the barrel forward like a rocket building up pressure against the breech-face, but does it make sense? The surface area of the breech inside of the chamber of the barrel is much bigger than that of the breech-hole, the force should be pushing the barrel backwards through recoil and it shouldn’t be possible for it to act like a rocket.

I have made similar but stronger designs earlier, holding the breech-face and the receiver-chamber together by bended steel instead of glue, those never blew apart and never forced the barrel to fly forward like a rocket. And in those designs the receiver-chamber were usually made out of a pipe, that pressure could more easily build up inside of compared to the cutted-out design of this particular receiver-chamber.

What’s your thoughts? Why did the gun blow apart?
 
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The pressure inside the chamber pushed the wood/breech apart. JB Weld is not strong enough to hold that amount of pressure. The burning powder would then seem like a rocket as it burned.
 
There is a reason that firearms designers like Mauser, Browning and Ruger were successful. Among other things, they understood the forces involved......


.
 
TX Nimrod said:
There is a reason that firearms designers like Mauser, Browning and Ruger were successful. Among other things, they understood the forces involved......
Click to expand...

Mal H said:
I'll try to be gentle - it's because you don't know how to make a gun.
Click to expand...

tlm225 said:
I sincerely suggest that you cease your experiments.
Click to expand...
I second all of the above statements. Especially the third.

I tried to follow your other thread, the one about "How strong are cartridges?" It was obvious to me from that discussion, based on the fact that a former Physics major (me) with graduate education in engineering (me) couldn't begin to understand what you were talking about, that you don't understand the concepts you're dealing with well enough to even explain your ideas, let alone bring them to fruition.

Let me try to put this into perspective. I'm an automotive hobbyist. Like many, I have a couple of "spare air" tanks. These are portable air tanks that I can pressurize from an air pump at a service station and take with me on a trail ride so that if a tire goes soft, I have a source of air to reinflate the tire. These spare air tanks typically hold about 125 to 150 psi, and they have safety check valves to ensure that they aren't pressurized any higher than that. Why? Because even at 150 psi, if a tank fails the results can be catastrophic.

Tire shops won't work on car tires that are older than 10 years. (Some won't touch a tire that's more than 5 years old.) Car tires are typically inflated to not more than 30 psi. Why won't the shops work on old tires? Because even at 30 psi they can explode and, if they explode, they can seriously injure the operator.

Now lets look at firearms. The mundane 9mm Luger operates at around 34,000 psi. (34 THOUSAND -- that's one thousand times the pressure the tire technician is worried about). The good old .45 ACP operates at "only" 19,000 psi -- so that's "only" 633 times more pressure than the tire technician is worried about.

I have no idea what you used for a load, but if it involved gunpowder I think we can assume it generated more than 30 psi. We also don't know what materials you used for your barrel or for your "receiver," but I'll bet it wasn't anywhere near the quality of 4140 ordnance grade steel. Trying to hold this thing together with J-B Weld and electrical tape? Yikes!

Please do yourself a favor. Whatever it is you are trying to accomplish ... STOP. You are going to injure yourself, possibly seriously and permanently. I wrote in your other thread that IMHO you aren't building a firearm, you're building a bomb. Apparently I was correct.
 
As I said in your other post "how strong are cartridges", I believe you are a future organ donor.
 
Ya know that guy that was gonna rocket his way to the edge of space to prove the Earth was flat a couple weeks ago?
This guy's starting to sound like the second cog in a Dirt Nap Theory!
 
I'm going to close this one now because I'm not sure there is anything else that needs to be said.

I trust that lessons have been learned and taken to heart. If not, at the very least, I hope that any future "testing" will be done in an environment where only the tester can possibly be endangered.
 
{Edited to deconfuse.}

I don't normally use my moderator superpowers to post in a closed thread, but I think the basic physics misunderstanding that lead to this disaster bears clearing up.

The problem was with the idea firing a gun would push its barrel to the rear. That does not happen. During firing, if the pressure at the breech is allowed to escape freely, the barrel and bullet briefly become akin to the combustion chamber of a rocket motor and the whole thing will be propelled forward absent the barrel's strong attachment to the receiver. Simultaneously, gas pressure is pushing back on the breech via the head of the cartridge case, trying to blow the breech off rearward. It succeeded in the gun in the photos. If it blows the breech back, the cartridge case will go with it until so much is exposed that the case bursts from the pressure.

The barrel tube itself only experiences a radial force perpendicular to its axis, so that, by itself, it doesn't try to move it either forward or backward. It's rearward movement depends on being attached to that which does experience rearward forces from pressure, and that is the breech, usually via the cartridge case head.

While recoil gives the impression barrels push to the rear, during the time a projectile is accelerating inside them and when gas is exhausting from the muzzle, the pressure actually pushes rearward only on the breech and forward on the bullet base, and the whole gun recoils to the rear because the breech is able to provide opposition to the force created by the pressure against it and transfers that recoil force to the whole gun.

Imagine a bolt rifle stripped of its locking and safety lugs and bolt. If you could make such a gun fire, the bolt would shoot out the rear and the bullet out the front and the rest of the rifle would experience no recoil.

Firing will not push the barrels back toward the breech. The breech has to be in place to be pushed against.
 
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