The thing is that black powder only explodes when properly compressed. So with any luck when you pour it in loose with lots of oxygen, if it were going to flair off, it would do so before you compress it, and place the projectile over the powder. So do not pour from the can, use a measure, don't place parts of your body over the hole as you pour it in. If it doesn't flash off, it probably won't go off from compressing it where the oxygen is being driven out. If there was an ember it should have gone off during the pour. Don't place your body in front of the ramrod, or the bore at any time.
One potential problem (if you are located in Can.) is that if your golf ball takes off at over 550 fps (?) and is one of the short overall length designs you may have built a prohibited weapon (or may have an unregistered regular firearm). How far does it shoot? If it's just a few hundred yards then it is well short of 550 fps. There could still be an issue of how heavily it could be loaded... Not trying to stir anything up, but this is a country where they ban throwing stars and blowguns.
What a collection of WRONG!
Come up with some actual cites for this pile of misinformation, or please, stop propagating such drivel!
Or let me rephrase that. Stop propagating drivel!
There is nothing anywhere that looks at the muzzle velocity of cannons. They are a matchlock, and are Prescribed Antique Firearms, and as such, are not regulated under the firearms act. Use one to rob a 7-11, and they are firearms under the Criminal Code, though. Same as a new made Flintlock or Matchlock rifle.
Black Powder IS an explosive, though a slow one, in the scheme of things. It will blow, when unconfined. Put 50 pounds of it in a pile and lay a fuse to it, if you don't believe. I've seen it firsthand, on an EOD range. Boom!
Black powder contains it's own oxygen source, so "compressing it where the oxygen is being driven out" has nothing to do with the hazard.
About the only thing you got right in here, is the risk of embers in the barrel, and " So do not pour from the can, use a measure, don't place parts of your body over the hole as you pour it in."
There is good reason that a bucket of water and a swab for the bore, was standard equipment on a muzzle loading cannon in the field or at sea.
Worth a wipe between shots to increase the lifespan of the loader!
Cheers
Trev