This is my Mauser / byf P38, it's dated 1943 & has a G suffix so dates it to july of that year ,just before the quality of finish went downhill, it's waffenampt 135 as is the magazine ,the gun has full matching numbers with no russian capture marks.
In 1942 the Mauser factory started the production of P38 pistols to fulfill the huge demand for these pistols by the German army. The secret code for Mauser is byf and is stamped on the slide just above the production year (last two digits).