I would do exactly as you're about to do.
No problems whatsoever. The brass, unless you make it crazy thin, will be more than sufficient for this.
The blanks are .22 and no, they don't go to any trouble to make them *quieter* though they do use smokeless powder which the old cannons did not have.
You might wanna pick up a pound of black powder for authenticity. (uh... a pound is good for a lot of shots... just sayin')
The .22 blanks would also be good for shooting. Not iron balls, but certainly plastic balls. That might be a real hoot.
I would make the fusing chamber to fit the .22 charges and use .22 charges to set off the black powder when I was using that. win-win!
Wrat