[SachAg]

I recently purchased a 1917 DWM. It has all matching numbers and also has British proof marks. The British proof mark is post 1954, as it is a crown over "BNP". The odd thing about the gun is that it has an aluminum magazine, not the typical wooden magazine. The magazine is numbered to match the gun and also has a small "42" above the 4-digit number. I assume the magazine must be a replacement. Does anyone know why a replacement magazine would be renumbered to match the gun? Would the renumbering have been done by the Germans or by a later gun owner?

Thanks for any help.