ORIGINAL: eldeguello
When you say "vise", I am assuming you mean a shooting rest of some sort. IF you are actually shooting from some sort of vise, that could be the source of the problems. NO rifle will shoot well from a hard surface or vise. Use a cushion between your rifle and the rest.
You have to clean these things from the muzzle, so rifling can get worn at that point. This is bad for accuracy.
The BAR I had (.308) would put two shots right together, then they'd walk off vertically. It was a Grade IV, so was nicely engraved. Too bad it wouldn't shoot. Got rid of it.
The vise I've had clamps to the side. However, I've also tried shooting off other stuff and it doesn't seem to do much better. The only time I've gotten it to group well was a thing I call a vise but I'm not sure if that's the proper term. Anyway, a buddy had it and you put the butt of the stock in it and it fit snugly around it. Kind of like the Caldwell Lead Sled's do. Then on the front it had a Y that the forearm piece rested in. I got great groups at 50 yards. Shot 6 shots and they all were touching. However, I can get decent groups at 50 yards in my vise thing I have. For some reason once I move out to 100 yards that's where the problem starts.
I will post a picture of what I have and am shooting from in a minute. It's kind of crappy but it holds it a lot stiller than I would be able to free hand. Even in sandbags I can't hold it but soo still. Less than like this. At least from the ones I've shot from.