Round shape in the bottom equal to the radius of the ball.

[oyvind]

Round shape in the bottom equal to the radius of the ball,
must be much stronger than one with a completely flat bottom with a small radius edge of the wall. like beer can mortar.
Or lose mortar pressure so quickly that it does not matter when the projectile begins moving?

Oyvind

[dan610324]

of course a full radius is the strongest

but if you shoot a projectile with another shape than a ball and maybe not a maximum load you can of course have another shape at the bottom of the bore .

good examples there is the beer can mortar

what diameter are you thinking about ??
what will you shoot from it ??
how heavy charges will you use ??

its a lot of different things that you need to consider before you decide anything .

[Double D]

The idea of a radius is to eliminate square corners to hide sparks or embers.

[seacoastartillery]

Round shape in the bottom equal to the radius of the ball,
must be much stronger than one with a completely flat bottom with a small radius edge of the wall.
Oyvind

     Oyvind,   While we certainly agree with you and Dan that a full radius is strongest, Double D. has a good point:

The idea of a radius is to eliminate square corners to hide sparks or embers.

     We must agree with him here and historically we can point to many Armstrong guns and seacoast rifles like the 8", 150 Pdr. Armstrong rifle that we studied at Fort Fisher, NC in 2006.  When you put a strong light down the tube, the 8" bore appeared to be flat at the end, and most of it was.  After carefully probing the edges of the bore bottom where it intersected the side of the bore we found that a 1.0" radius existed, but most of the bore bottom was shaped like a pie tin.  With 35 Lb. powder charges and 150 Lb. solid bolts, this very knowledgeable ordnance company wisely eliminated stress risers, (sharp corners) and  provided an easy shape to keep clean.

FYI,

Tracy and Mike