It may need a test case, but I would say no...
State laws defining "firearms" (609.666, 609.02, 97A.015) fall into several classes:
1. Federal law, basically a cartridge-loading arm.
2. Or expels projectiles by action of an explosive (nevermind that smokeless powder is hardly an explosive, legislatures don't know that much), or
3. Expels a projectile by means of an expanding gas (which would include muzzleloaders).
Case law has convicted felons for carrying a BB gun.
A convicted felon barred from carrying a firearm broke the law when he started toting a BB gun, the Minnesota Court of Appeals has ruled.
John Fleming Jr. couldn't legally carry a gun because of two felony assault convictions, so he packed a BB gun instead.
Ramsey County prosecutors decided Fleming was splitting hairs and charged him with unlawful possession of a firearm.
Fleming won when a Ramsey County District judge threw out the charge, ruling the statute doesn't apply to BB guns. But the appeals court ruled prosecutors could again take aim at the two-time felon.
The appellate court reinstated the charge against Fleming, finding that a firearm is "any gun from which a shot or a projectile is discharged by means of explosive, gas or compressed air."
Fleming is accused of carrying a black metal BB gun that discharges a pellet by means of a CO2 cartridge.