I have received an AR15 as part of a trade and want to put a scope on it for some fun shooting when I get it. I have not had anything to do with AR15s yet and was wondering if the scope rail is just an ordinary picatinny rail? Reason I ask is I have seen lots of mounts listed as being for AR15s, just didn't know if my regular mounts will fit or if I need to spring for another set?