This is a high quality all steel 5 round aftermarket magazine for pre 1933 historic Mauser .22LR military trainer and sporter style (Mini K98) rifles.
This is the angled base type, which mounts up against the trigger guard where the magazine catch is located. Not to be confused with later 'B' versions with curving magazines mounted forward of the trigger guard.
It is fully strippable for cleaning and has the correct indent in the machined steel follower.
