As the description says it is a "Mauser" action dated "1917" with a four digit serial number, I suspect it to be an ex-military Gew98 action from WW1. German military rifles then were numbered like this: On top of the receiver ring the factory "Mauser", then year "1917". Each maker and year started over with number "1" and continued to "9999". then a letter was added, "1 A" to "9999 A" and so on.