Shooting free hand or off a rest, one's body would absorb a lot of recoil.Ok, I don't mean to sound like I'm on your case and I might be outright wrong, but somehow I can't help but think that shooting a crossbow that is held solidly in a vice may be hard on the bow.
All my shooting with various brands and series of crossbows have been
locked into a high quality rifle jig. No damage here with many thousands
Wishing you all the best.