I've tried some "soft" cast bullets (12 bhn) from two different suppliers. Basically, they suck in the XVR. At low (800-1000 fps) velocities they "go that way" and keyhole the target when they actually hit the target.
Missouri Bullets has some hard cast (18 bhn?) that I've been wanting to try. The next time I place an order, I'll try to get a few to try.
What gun / barrel do you have? My XVR has the gain twist barrel. It doesn't seem to stabilize a slow/soft bullet worth a crap.