In the States, as here in Canada, the length restriction is 26" overall. Here in Canada, they must also be obviously meant to be fired by the use of both hands. Thus, any barrel length on a bolt or lever gun is OK as long as it is 26" or longer, overall. I would suggest a short barrel and no forend might lead to charges, but if having a forearm, the barrel could be 12" or 10" and still be OK, as long as the gun is overall 26" or longer and also meant to be fired with 2 hands.

I suggest that larger bore sizes barrels can be shortened more than smaller bores and still maintain good killing power. I suspect a 10" or 12" .30/30 would be pretty poor as the velocity drops off below what makes the bullets expand and create damage to tissue however a 12" .44mag, .44/40 or .45 Colt on the other hand, will still make a wonderful killing weapon on most game, expecially from a M94 Winchester or Marlin.

Better yet, a .45 Casull or .460 S&W on a Big Bore 94 action or Marlin 94 that's capable of being loaded to 44,000psi. would really work well, in the bush - like right around here.

Hmm- I have a doner (1978) .375 Big Bore that's not doing much right now. By itself, at 20", it sure worked well on a couple moose.