Matt- if you go to auctionarms.com, on their home page, there is a link to a "for fee" firearms appraisal company. Have NO diea what their fees are- you can ask.
A flintlock

holds a bit of flint rock in the cock. When trigger is pulled, spring forces the flint down the frizzen, scraping sparks into the priming pan.
A later and more reliable arm was the caplock. A small metal cup (the cap)holding priming compound was placed on the gun's nipple. The hammer strikes the cap, exploding it, send a jet of flame through the hollow center of the nipple, and into the powder charge.
If the opening in the end of the barrel is nearly an inch in diameter, this would be more likely to be a shotgun, but the extreme light weight would make a shotgun VERY punishing.
If you have not done so, please check and see if your arm is still loaded. Take the ramrod (or any gun cleaning rod long enough to reach from the muzzle ALL the way down the barrel to the nipple) lay it against the outside of the barrel, one end at the nipple, other end extending past the muzzle. mark the end at the muzzle (wrap of tape) and and then insert the rod into the barrel. It should be to within a half inch of your tape. If the rod presses against something an inch or two- or more- before it goes all the way down- you may still have powder and shot in there. It happens.
If so, do not panic, but do not try to shoot it out- a gunsmith can safely pull the charge using a rod and a tool called a worm.