Sounds like you have a M1912/16 carbine. It was a mid size, short rifle of sorts, to serve all purposes. These are the most common variation in this country. The stud on the barrel was for the rear sight to flip over on to use as a "battle" sight. Is the stock still the full length of the barrel, are the hand guards still on it with the nose cap/bayo lug? Go to our website main page and check the photo section to see if it looks like any that are there.