Deck Gun

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fredrosse
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Deck Gun

Post by fredrosse » Sun Nov 30, 2014 9:10 pm

Many Steamboats carry a muzzle loading cannon, but as I recall the steam age brought breech loaders firing fixed ammunition to the sea, so I am in the process of modernizing.

Got a 12 Gauge rifled barrel on e-bay, and started machining the receiver today from a 1-1/2-8 nut. The deck gun will fire ordinary or 3 inch magnum 12 gauge shells, and will be using the classic interrupted screw breech mechanism. Another wintertime project.
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Nut with threads milled away for interrupted screw arrangement.
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Lopez Mike
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Re: Deck Gun

Post by Lopez Mike » Mon Dec 01, 2014 2:57 am

Will you be firing blanks? The breech pressure with real loads, especially slugs, is higher than you might expect.

There are two types of blanks ( I speak from experience as I was the committee boat for sailing events for many years). 'Popper' rounds which are smokeless and not that loud, and black powder ones which are fairly loud and make a very satisfactory cloud of smoke. The drawback to the black powder rounds is that you must take the gun home and wash it well with soap and water followed by WD-40 or some such gunk.
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fredrosse
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Re: Deck Gun

Post by fredrosse » Mon Dec 01, 2014 5:33 am

Blanks most often, crackers too, but I will certainly also try it out at the range with slugs.

This breech mechanism will be plenty strong for the pressures produced by any standard shotshell loads. SAAMI standards indicate 11,500 PSI Maximum Shotshell Pressure for 3 inch Magnum Slugs, with Proof Loads of 19,000 PSI. The most highly stressed part of the mechanism is the breech threads. Calculating with a 20,000 PSI Proof load, the shear stress in the breech threads is only 13,300 PSI, not much even for mild steel.
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Re: Deck Gun

Post by Jack Innes » Mon Dec 01, 2014 3:38 pm

I am sure you will find the breech pressure decreases appreciably as the barrel becomes shorter. The rifling will increase the breech pressure though.

Have you considered the legality of the finished gun? I know the regulations in many states are much more sensible than ours but here in Canada such a breech loading gun, using available ammunition & an overall length of less than 26" would be a restricted or possibly prohibited weapon. You could maybe own it at home with proper permits but could not have or use it in public. Most muzzle loading, black powder cannons have a muzzle velocity slow enough to be in the same class as air pistols & therefore not regulated here.

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fredrosse
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Re: Deck Gun

Post by fredrosse » Mon Dec 01, 2014 7:32 pm

"breech pressure decreases appreciably as the barrel becomes shorter" It is my understanding that peak breech pressure should be entirely independent of barrel length, as peak breech pressure occurs in the first inches of projectile travel. Granted the pressure within the barrel decreases rapidly as the projectile travels down the barrel.

The deck gun will be legal according to USA Federal and Pennsylvania Law. As a matter of fact the cannon, with 20 inch barrel, will be longer than 26 inches overall. I find it interesting that real Gatling Guns, firing commercially available ammunition, are also legal here without any special licensing. Although they can fire well over 600 cartridges per minute, they are not legally considered as "Machine Guns", since the shooter has to operate the crank.
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Re: Deck Gun

Post by S. Weaver » Sat Dec 06, 2014 1:58 pm

Fred, can't wait to see it. We'll be giving you a wide berth ... Let me know if you would like a Letter of Marque; I could probably draft one up for you. :D
Steve
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