How 'bout some ideas for making approx. 9.5-inch mortar balls?

[Double D]

Do not use anything around the circumference of that shot to make it fit tighter.  You will drive pressures up and and maybe even break something. 

Do make some sort of sabot to ride the bore behind the shot. 

You jam one of those shot in the bore going in you are going to have a nightmare getting it out.  You jam it coming out your family could have a night mare.  Don't care how many times you got away with it in the past it's still dangerous. 
 
The internal ballistics of cannons is vastly different than  some  .54 cal muzzloading rifle.  It is a genie you do not want out of the bottle.There is a reason the originals were not patched and this is it.

[cannonmn]

We should probably call it a canvas sabot.  The idea actually came from shooters at Ft. Shenandoah.  They had read about how the CSA used their Austrian howitzers at Gettysburg and elsewhere.  I have to look up the exact bore diameter on those bronze howitzers, but the South used 24 pr. howitzer shells in them, even though their existing 24 pdr. shells were too small for the bores of the Austrian howitzers they had imported.  They used greased canvas around the shells and fired quite a few into Union lines, apparently without incident.  I haven't read the accounts myself, but I'll look them up.

I agree, you certainly don't want any material ahead of the projectile that could get jammed between the projectile and the bore.

[cannonmn]

This must be what they were remembering.  Looking in the book FIELD ARTILLERY WEAPONS OF THE CIVIL WAR by Olmstead et al, University of Delaware Press, Newark DE 1983, pp. 191, regarding Austrian howitzers:

A Confederate ordnance manual gives the bore of these as "5.87, instead of 5.82."  It continues "By having the balls enclosed in canvas, the ordinary ammunition for the approximate calibres in the C.S. service may be used with these ... howiters."

[Double D]

"By having the balls enclosed in canvas, the ordinary ammunition for the approximate calibres in the C.S. service may be used with these ... howiters."

Enclosed is the optimum word.  Not just a patch. You want that canvas to be like part of the ball and move with itl.  And not tight in the bore either.   Remember a 24 PDR ball was 5.68 inch in diameter to fit in a 5.82 bore. 

[cannonmn]

Apologies to anyone looking for the NSSA mortar competition video, mine won't be uploaded to you-tube until I find out how to fix my "Windows Movie Maker."  The video clips came out fine, but the program I use to knit them into a video that can be uploaded is kaput.  Workin' on it.

[lance]

Apologies to anyone looking for the NSSA mortar competition video, mine won't be uploaded to you-tube until I find out how to fix my "Windows Movie Maker."  The video clips came out fine, but the program I use to knit them into a video that can be uploaded is kaput.  Workin' on it.

Glad you're working on it, i'm waiting on it