Sean-A "squirrel gun" commonly referred to a small calibre rifle. You are right that a single projectile weapon is preferred to a shotgun due to the more limited damage to the meat. In addition, ammunition for a shotgun was and is more expensive, and the shotgun has a shorter effective range. The squirrel rifle and the shotgun were the most commonly owned private firearms, and were thus the primary weapons of the State Guard. These firearms, including shotguns, were muzzle loading. As for the squirrels in Iowa, either in trees or on the ground, I have doubts about scaring them to death. Most Southern boys shoot for the head, even if it ruins the brains.