IF there is a KB (KaBoom) the gasses vent in fairly predictable directions. The receiver is not going to be a factor. Gasses vent down, through the magazine. Or back, into/through the bolt/carrier to the top cover that is stamped sheet metal and not very tough. Once the gasses enter the open areas of the receiver (beneath and behind the bolt/carrier) the pressures drop quickly as the volume of area available greatly expands. I believe the doubling of the area/volume, reduces the pressure by a factor of 4. So twice the area = 1/4 the pressure.
To more directly answer the question, IMHO Milled Receiver AK's are no "Safer" than stamped versions.
No safer one way or the other. Many internet armchair experts will debate this until doomsday, but either is safe ( unless you try to make your own proof loads or get something plugged in the barrel! )
Milled receivers in SKS or AK are NOT ANY SAFER! The Milled steel design's gives the impression of being stronger, a bit heavier, but the years all have proved that Stamped steel was brough out, as soon as the Russians were able to weld and perform Stamped steel, Not any Weaker, easier to produce and Just as Long Lived a Design! This is anohter Item where what feels better, really isn't any better or safer, if just feels that way?