Looks like a Model 18 Smith, I'd guess Mk70. I picked one up a few months ago and really like it. Ejection after a cpl cylinders full is tough, but a good brush out with a bronze brush cures it fast enough. How's it shoot? Mine's comparable to my M41 Smith, tho my 73 yr old eyes are probably to blame.
For a fun and demanding test of your slow fire technique, try charcoal briquettes perched on an fence rail from 8-10 yards...and hey, there's no clean up! Spent non-reloadable shotgun shells are another good tgt. Standing upright on a piece of fence rail or rolled along a dusty two-track, they're fun to work over, double action.
Another good exercise is a soup can suspended from a piece of 14 ga hot wire fence wire. They swing nicely and are a breeze to reset when you clip the support wire.
Rod