I agree that smokeless will probably only fizzle in the absence of a pressure build up such as would happen if a projectile was placed in the bore but loading it the same way as a black powder blank load would not produce an exploding boom that one expects to hear from a cannon.
Smokeless is generally clean, quiet (relatively compared to black powder,) and VERY HIGH PRESSURE with very little smoke when it goes bang. Smokeless is much harder to ignite (made to be ignited by a hot primer directly next to it.) I can think of all sort's of problems offhand such as ignition failure, hang fires, partial ignition, low noise report, unreliable, likely unsafe (if seeking a loud boom) etc.... and you will probably need a small charge of black powder to reliably ignite it in which case you might as well load it all with black powder. It's everything you don't want in a signal cannon.
VERY BAD FOR FUN DON'T LET THAT SMOKELESS POOP YOUR PARTY.
What worries me is someone will attempt to create that boom with smokeless by trying various ways to introduce pressure build up not knowing that success in doing so will create a very dangerous pressure spike that could result in a deadly explosion and with a smokeless powder type that is not supposed to be packed (my understanding is some brands/types can and others cant') it would create even more deadly pressure.
Think about this. Black powder firearms including cannons, whether loaded with blanks or not, produce much less pressure and power than their smokeless counterparts yet create a MUCH LOUDER EXPLOSION and smoke (extra smoke is added fun) despite being a MUCH weaker propellent.
I don't think using smokeless powder for the exclusive purpose of creating a loud boom in a blank load, or any load it's was not designed for, is a good idea. In fact I think it's dangerous.
I am not a smokeless powder expert but there are all sorts of different smokeless powders out there with different burn characteristics. Your typical smokeless load is not designed to be a blank noise maker and when dealing with smokeless it's best to strictly stay within the safe parameters of it's use.
These are the reasons I am reluctant to comment on this.
To avoid any civil or criminal legal liabilities I would stick with good old fashioned black powder which is much better and fun (and less dangerous) than any smokeless load any time in a cannon.
In this world there are often a few different ways to do things but this is not one. Smokeless is just the wrong stuff to use for what you want. It's not worth your time and effort.
Please if you can, if I may suggest, devote the valuable time and effort into getting some black powder. You are at an advantage since a lower quality black powder that creates more smoke and soot may make this thing even more fun to shoot for less money.
Are you having any problems obtaining black powder ?
What type of black do you use 2f or 1f ?
