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 Post subject: Deck Gun
PostPosted: Sun Nov 30, 2014 9:10 pm 
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Joined: Fri Nov 20, 2009 5:34 am
Posts: 1430
Location: Phila PA USA
Boat Name: Margaret S.
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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File comment: Nut with threads milled away for interrupted screw arrangement.
Receiver.jpg
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 Post subject: Re: Deck Gun
PostPosted: Mon Dec 01, 2014 2:57 am 
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Joined: Wed Dec 07, 2011 6:41 am
Posts: 1458
Location: Lopez Island, Washington State, USA
Boat Name: S.L. Folly
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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 Post subject: Re: Deck Gun
PostPosted: Mon Dec 01, 2014 5:33 am 
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Joined: Fri Nov 20, 2009 5:34 am
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Location: Phila PA USA
Boat Name: Margaret S.
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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 Post subject: Re: Deck Gun
PostPosted: Mon Dec 01, 2014 3:38 pm 
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Joined: Mon Sep 30, 2013 9:12 pm
Posts: 84
Location: Brooklin, Ontario, Canada
Boat Name: Mazeppa
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.

Jack


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 Post subject: Re: Deck Gun
PostPosted: Mon Dec 01, 2014 7:32 pm 
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Joined: Fri Nov 20, 2009 5:34 am
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Location: Phila PA USA
Boat Name: Margaret S.
"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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 Post subject: Re: Deck Gun
PostPosted: Sat Dec 06, 2014 1:58 pm 
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Joined: Mon Sep 26, 2011 4:23 pm
Posts: 317
Boat Name: SL Iona
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

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