Re: help identify old shotgun
The star-over-PT is a French proof. Smokeless, from 1900. The 70 should be the chamber length, in millimeters, which is 2 1/2 inches, so do not fire modern ammo in it.
You can either buy 2 1/2 inch shells, which, while scarce, are out there, but quite expensive (around 10 to 15 bucks a box) or have the chamber lengthened.
2 3/4" shells will fit in a 2 1/2 inch chamber, and fire, but they won't open enough, so the pressures will skyrocket. Bad juju.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.