A .38 S&W RP (it is called the Regulation Police Model) with SN 57xx probably shipped in early 1918. On my list is 56xx which shipped in 3/18, also 65xx shipping in 4/18. It will be safe to fire with any .38 S&W ammunition you can find, except .38 S&W ammunition is somewhat difficult to find, most dealers will not stock it. You may have to have it special ordered by a dealer or ordered from internet sources. And it is not cheap. It is not the same as .38 Special ammunition.