This is a commercial version of the M1917 Enfield. It was produced, from what I could find on it, from 1921-1940 in serveral models. A carbine (M30R), a 22 inch barreled version (M30A), and a M30S with a 24 inch tube. I also recall the Express as being a 'higher grade', but that's from my memory, a very poor thing to rely on. Sounds as if you have a fine old sporter.. If the bores up to it, why not take her afield again?? They are quite strong weapons and the safety is positive in action.. Have it checked by a gunsmith, out of respect for a 60-80 year old rifle, and sight it in.. The Lyman receiver sight you describe is very functional. good luck to you and yours and a Happy New Year!!! from the gunnut69
