Keep in mind that some of that WWII axis ammo was loaded by slave labor, and the folks forced into slavery would send a few extra powder charges into the batch to blow up in the users face.
Granted in a true Mauser it would need to be on hell of a bang to cause any damage endangering the shooter, it would be a shame to fall victim to 65 year old sabotage.
That would be nearly impossible as the case is nearly filled to the brim with powder as it is with a normal charge. I am also certain that sabotage did occur, but in the many thousands of surplus Axis rounds I have safely fired and the tens of thousands that have been fired by those I know or communicate with via the web I have never heard of something like that happening. The real danger I have seen is when a reloader accidentally loads a rifle round with pistol powder or another powder with a grossly different burn rate.
Don't want to tell anyone what to do or be a jerk so by all means do what you feel comfortable with. Sorry for the hijack, I will shut up now!