[gf45acp]

As you do not know the history of the ammo, I am going to step out on a limb and guess that it may just be in the PMC box and is a box of HOT reloads. The .44 mag is the correct ammo for the Super Blackhawk. Deep six the remaining ammo.
I have shot many thousands of rounds of PMC ammo without a hitch.
As to the gun, the Super Blackhawk is a strong revolver. As there is some question as to if the problem is the gun or the ammo, I would take the gun to a gunsmith have have it checked just to be sure. A .44 mag going kablooie is not something I want in my hand. If you don't have the proper tools you are not going to be able to check for things like oversized chambers that xring mentioned.
There is also the possiblily that your dad may have had custom work done to the revolver, and it is not in it's original caliber. Perhaps a Ruger expert on this site can correct me if I am wrong, but in that time frame I don't believe that the Super Blackhawk was made in anything but .44 mag. The cavat is that the Super Blackhawks have been the basis for many custom conversions.
A friend recently showed me a Dan Wesson .357 mag that his father had that had a S&W barrel installed in it! No known history, so who knows if the gun is safe without an in person inspection by a gunsmith.
It will cost you a few dollars, but have it checked in person by a smith.