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Old March 15, 2009, 05:23 PM   #1
ADB
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Hi everybody. Question about building a shotgun.

I've been lurking around here for awhile now, but I had a question about a project I've been considering, and I thought this would be by far the best place to ask it.

I was thinking about trying to build a basic shotgun for fun and usefulness. This would be a small bore (.410) single shot weapon mostly intended for varmint killing: snakes, and the weasels that attack the chickens.

Being that this is my first project, and it's a varmint gun, I'm trying to make it idiot simple and relatively lightweight. My question is about the barrel itself. Considering the low power nature of what I'm building, it necessary that I buy a "real" barrel, or could I improvise one out of something else? Say, steel pipe, or 1" steel bar with a nice reamed hole to the proper diameter? Obviously varminting this thing is probably never going to be used at more than 10 feet or so, so accuracy isn't a big issue. Pipe would be far easier (I'm not even sure how I'd ream out a ~2 foot length of steel bar), but I've heard people suggest that steel pipe would split or explode under the force of a .410 shell going off.
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Old March 15, 2009, 05:39 PM   #2
rantingredneck
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Considering that a single shot NEF can be had for about $120.00 and will outlast you to be handed down to your heirs, I'd say go that route and forget the steel pipe and such.

Just my .02..........
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Old March 15, 2009, 05:49 PM   #3
Jim Watson
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Buy it or build it, just remember, the barrel must be at least 18" long and the whole gun must be at least 26" long to be legal in the USA.

I would want at least high pressure tubing to make a shotgun barrel. A 20,000 psi tube with 3/4" o.d. will have a .438" i.d. which will probably work ok, considering that .45 Colt - .410 shot combos are feasible.
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Old March 15, 2009, 05:55 PM   #4
Sevens
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Quote:
Considering the low power nature of what I'm building
Here's your first problem-- it's small bore for a shotgun, but there's nothing low power about it. It's still going to need to handle 15,000 PSI. That's the same as: 28 gauge. And 20 gauge, and 12 gauge and 10 gauge, too.

I'm not sure about the Federal laws with regards to building your own firearm. I'm sure it's legal-- but not without some kind of hoops to jump through. And as was already said, there's not likely to be any way for you to build something nearly as effective and operative as one of the cheaper new ones... and at a gun show or swap meet, you could find a beat up cheap one for chump change.

If it's simply the idea that you WANT to build something to prove you can do it, I can understand that. But think about what's happening in the chamber and where your face is in relation to the chamber before you go forward with the project.
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Old March 15, 2009, 11:08 PM   #5
ADB
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Jim, that will be remembered at all times, and I do appreciate the reminder.

Sevens has my number--it's not so much because I NEED another shotgun (I have a 12 gauge already) but I found the idea of being able to do it interesting. Maybe it'll prove out to be impractical, but I wanted to at least investigate it as a possible project.

Re: the pressure issue, maybe I've spent too much time looking at rifle information, but it strikes me as odd that a .410 would produce as much pressure as a 12 gauge. After all, you're propelling a much lighter load at the same relative velocity, no? I'll look into high pressure steel pipe or tubing.

Last I heard, it's legal to build your own gun, and you don't need paperwork unless you plan on transferring it to someone else. I could be wrong, though.
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Old March 15, 2009, 11:31 PM   #6
Sevens
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Cartridge pressure does have to do with the weight of the load, but it has just as much to do with how large a space the reaction is taking place in.

Take a 9mm and a .38 Special for a quick example.
Both can be had in similar bullet weights, but the .38 Special is more typically loaded with a 148 to 158 grain bullet. A 9mm is typically loaded with a 115-125 grain bullet, but the heaviest loads go up to 147 grain.

The 9mm does all it's damage in a tiny case that's like HALF the size of the .38 Special. It runs at pretty much twice the pressure. That's how that tiny little caliber can out perform a .38 Spl, that by looks alone, is twice as large.
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Old March 16, 2009, 09:09 AM   #7
PetahW
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IIRC, The only rifle cartridge with operating pressures as low as shotshells (12,000 psi) are .22 rimfires - since most older CF rifle cartridges are about 28,000psi, and modern CF's go to 50,00 + psi.

Used single-barreled .410's can be readily found for less than $100, and are easily altered to your taste.



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Old March 16, 2009, 09:20 AM   #8
Jim Watson
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Actually, .410 chamber pressure runs somewhat HIGHER than 12 gauge. The load is lighter but because the bore is much smaller, it takes up more depth in the shell and bore. This is comparable to high sectional density in a rifle bullet, which is a pressure builder. Also, the .410 has more wad contact with the barrel per ounce of shot, increasing frictional resistance; which probably increases pressure somewhat.
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Old March 16, 2009, 11:31 AM   #9
brickeyee
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Quote:
Re: the pressure issue, maybe I've spent too much time looking at rifle information, but it strikes me as odd that a .410 would produce as much pressure as a 12 gauge. After all, you're propelling a much lighter load at the same relative velocity, no? I'll look into high pressure steel pipe or tubing
.

The velocity from a firearm is the pressure generated by the burning powder times the duration of time the pressure is applied.

It gets hard to actually do the calculations since the pressure is NOT uniform for the length or barrel travel.

The PEAK pressure is what causes guns to fail.
Peak pressure by itself is NOT an indicator of velocity.
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