I have a .44 mag with an 8" barrel I use for deer. MD does not restrict the caliber you can use for deerbut does say that the gun must produce 700 ft/lbs of energy. See below..

Modern and muzzleloading handguns may be used to hunt upland game (except dove and woodcock) and forest game (except turkey), woodchuck, fox, coyote, opossum, nutria, fisher, skunk and raccoon. However, modern handguns may be used to hunt deer only in those counties where the use of a breech-loading rifle for deer hunting is permitted with the exception that modern handguns may be used to hunt deer throughout Frederick County. Any modern handgun used for deer hunting must have a barrel length of 6 inches or more and use ammunition which produces a muzzle energy of 700 foot-pounds or more.