I don't expect the gun to work; it seems to me that if Voldemort had a ritual to give people properties of magical creatures, he would have given them to himself, and firing a gun at a troll three times would not be terribly effective. But would his body recreated from his blood through this ritual have those features? Uncertain. But shooting a troll three times would still give you enough time to close the distance, or cast a spell on him before he could fly away, or so on.

[edit] As people pointed out below, I forgot about the temporary nature of the spell without the stone.

It is also interesting that the horcrux spell can be cast for others (or is he doing other mind magic at the same time?).