S&W M&P .38 Special DOM?

I just bought it for $160, s/n 3184xx, about 60%, a few small patches of rust, shot a lot and carried a lot, the right grip has about 90% of checkering worn away. Came with a very good quality holster much newer than the gun. Belonged to my uncle and said to date back to 1920s. Would appreciate knowing actual DOM and any other comments.