This WWII German MP38 was manufactured by Erma (Erfurter Maschinenfabrik) in 1940 shortly before production was discontinued in favor of the MP40. This is a rare unmodifified example with the original "hook" style bolt. 

The MP38 is almost identical to the MP40, a little heavier, and most parts will interchange. The difference, however, was that the MP38 was almost fully machined (instead of stamped) and was made with an overall higher quality fit and finish. 

As for the rate of fire, the MP38 and MP40 share the same rate of fire, around 500-550 rpm depending on the ammunition used and the condition of the recoil spring. The ammunition used in this submachine gun was the standard 9-mm Parabellum cartridge, used in all German pistols and submachine guns. This was a rimless, straight-case cartridge with a round-nose, jacketed bullet. It came in cases containing 4,160 rounds, packed in multiples of 16 rounds in cartons and packages.

The added weight of the machined parts and the extra cost associated with manufacturing them led to a relatively short production run as the Germans put new sheet metal stamping techniques to use with its replacement, the MP40. The MP40 was actually slightly more expensive and cost 60 Reichmarks per unit while the MP38 cost 57.  

When Germany launched the attack on Poland (“Fall Weiss”), about 8700 MPs were listed in the inventory reports of the units. The MP38 stayed in service till the end of the war, but most of them were modified with an improved safety from the MP40.