Yes he (or whoever) did use a 357 according to reports.

Gravano said to use a revolver on a hit so you won't have to risk the gun jamming. I think he said he liked 38 specials but i'd go with Nicodemo on this one. If your going to use a 38 special you might as well use a 357 for the extra pop.

You can shoot 38 specials out of most 357 revolvers but you can't shoot 357's out of a revolver that was made to fire 38 specials. So you might as well just go with the 357.