For the powder chamber. Max is 2oz fg per inch if I remember correctly? that is 17oz. I want to be able too send it far but I don't think I need a 17oz powder chamber. or do I? What would be a good size? I have 600+ yards to play with now. When I figure wall thickness should I just go by the inner plug and not consider the outer tube? I would like the option to use the max safe load if I ever find a safe place to do it. Would a 2 5/8" powder chamber deep enough to hold 12 oz's be ok? Would that empty place create any problems when shooting lighter loads? Again I thank everyone for sharing what they know.
The base plug you are talking about is 9 inches, so the max chamber diameter would be 3 inches. 2 oz. per in a 3 inch chamber is 6 oz, not 17. In a mortar the powder chamber is the bore size.
In a bore this large and with a projectile this heavy you want to be sure you use
Cannon grade powder. Pressure will be substantially higher with Fg and should not be used for large cannons. With Cannon grade use 3 oz per inch or 9 oz. max load.
There is no advantage using the higher pressure Fg powder in these guns.
In this application there will be no adverse effect from the air space. The base of the projectile is round and not flat and is in the expansion chamber where the pressure hammer is dispersed.
Make yourself a dummy plug plug of wood. I would drill a 3 inch hole through a 2" x 4". Fill the hole level full of Cannon grade BP and then weigh the powder. Divide that weight into 9 oz maximum weight. Multiply that number by the thicknes of the 2 4 and that is how deep your chamber must be to hold that maximum weight.
(George-check my math please...
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