For sure it's not safe to chew tabacco and blow down your barrel.

I don't recall ever seeing D. Boone or Davy Crockett blow down their barrels in a movie didn't they like to wet their front site ?

V.M. Starr liked to spit and blOw down his muzzleloading shotgun barrels....not a very safe practice. I guess he should've used a tube or a small section of garden hose.

http://members.aye.net/~bspen/starr.html

Check out the link above....carefull V.M. Starr was very unsafe and evidently knew nothing about muzzle loading shotguns.
Lifes a gamble.