Frame and slide point to older than Gen 3
Grips narrow it down to "not Gen 1" (so probably Gen 2)
Lack of pins and markings muddy the identification fairly substantially but the shape and size rule out at least the 19, 23, 24, 25, 26, 27, 28, 29, 32, 33, 36, 38, 39, 40, 42, 43, 45 and 48 (all of...