Quote from the current 2005 Hunting Abstracts.
"During the shotgun season hunters may use shotguns not larger than 10 gauge, bows and arrows, or muzzleloadders, including modern muzzleloader, muzzleloaders with telescopic sights, and sabot rounds in muzzleloaders, including hinge action muzzleloaders."
Now here's where it gets tricky.
"Muzzleloader season - Limited to shoulder-fired muzzleloaders .44 to .775 caliber; barrel length 18" or more with only one barrel operative. In-line ignition systems permitted, providing the rifle loads from the muzzle. Hinge action muzzleloaders are not legal. Single projectile only (no buckshot). Sabot rounds, 209 primers and scopes are legal. Powder limited to black powder or approved substitutes. Firearm is considered unloaded when cap or pan powder is removed.......
So, from this it looks as though during shotgun season, you are free to use any style of muzzleloader, but during muzzleloader season, you are prohibited from using "hinge action".
Man this shit is confusing..
For more info, check out the abstracts here.
http://www.mass.gov/dfwele/dfw/dfwpdf/dfwab05.pdf
Adam