Yes it looks like dual hatcher holes.I think it was drilled to provide an escape for gas if a case ruptured. But then somebody came along and put a plug in the hole. The plug bothers me more than the hole, if a case ruptures the screw might become a projectile. The hole itself does not appear to be in a critical area that weakens anything.
The no.4 vent hole is on the left side of the receiver just above the stock line, same side as a right hand shooter’s face would be on.Can't imagine why anyone would do that for gas escape? I think the mauser is designed for gas from a blown case to flow back along the bolt raceways and be deflected upwards away from shooters face by the bolt shroud.
Maybe I'm mistaken?
The holes look to be at 45° from where the bolt lugs lock up, so, were it me, I would probably shoot it.As a carryover from my post in the Husqvarna thread.
This is a Husqvarna in 8x57 that seems to have threaded holes drilled thru the receiver.
Why was it done ? deactivation ? strange scope mount ? .
Altho the real question remains.... Would you shoot it?