Vlim and John are both correct. The magazine is for a later manufactured pistol and the lack of proof marks on the right side of the receiver reduces the value. How much of a reduction would depend somewhat on the buyer. A nice clean 3rd variation 1937 Mauser S/42 without a matching magazine can go for as much as $1800 (at least the one I sold last month did) but one like yours would drive me to think that maybe $$1,000-$1100 would be close because it is so clean. Again it all depends on the buyer.
Lyn

how does it shoot?........