I was given a mauser by a family member recently...I was just needing to check a few things on it before I put money into it. (1) the rear of the receiver has been filed down to accept a turn down bolt which has been welded on...is this safe or should i treat the metal? (2)Its a spanish Armas 95, stamped 99 on the receiver and then restamped 99 in slightly larger numbers over the old stamp...this means? (3) the barrel is relatively short, I think around 17 1/4" long and it only steps down once...is this a carbine or a hack job on the barrel? (4) It shoots really really well, from prone with the existing barrel i get consistent 1" groups at 100yds, the barrel is in really good shape. Anyway thanks for the time and hope you gents can help me a little.