I am not familiar with the Vanguard finish, but the Mk V W'by finish is not poly. It is a fullerplast two part epoxy finish. It is one tough muther. I did a stock for a guy with years of scratches and dents...and that is hard to do with that finish. I started with 150 grit which didn't even cut through the finish. I had to go to 60 grit on a power finish sander.

Good luck.