Well, a little progress.

[/url]
Both are 304 stainless.
The left one is .50 cal. with a cast ball in front.
The right one is about .30 - .32 cal with a #0 or #00 buckshot.
Both started with 7/8 diameter stock.
The trunion is brazed on. Not something I'd do on a mortar that would be used for real.
THE REAL advantage of doing these two is to figure out the process steps and the fixturing needed to locate accurately for each operation. After the third one or so, the process is much easier.