STOP. No, really- STOP! DO NOT CLEAN UP THE RIFLE.
What you call crud/ dirt collectors call "patina". I have seen dozens of high value collectable firearms destroyed by "cleaning" them. Other than light oil, and rubbing (gently) with a clean cloth, DON'T.
Any restoration should be done by an experienced restorer. Otherwise, it is like trying to "restore" a Monet oil with a can of Rustoleum.
This is a link to a company that sells reproductions- may help identify what you have. VERY possible that it is a Civil War firearm.
Civil War Reproduction Muskets - Taylor's & Co., Inc.
Important PS- have you checked that there is not a load in the gun? If not, use the ramrod to check. If you do not know how, send me a PM.