I've known for a while that PT&G offers a piloted counterbore for cutting the .705 bolt nose recess in Rem 700 barrels, and have contemplated acquiring a couple.

Looking at them on PT&Gs web site I see that they offer a straight and stepped version. Can someone explain the difference?

The stepped version you can only cut the .150" depth needed and then will cut tenon and chamfer as you go deeper. The straight one cuts as deep as you want or need to. Say if you wanted a couple thousandths more depth because bolt nose to lug was out of spec and a couple thousandths too long.

Every bolt nose recess is slightly different based on the bolt nose dimensions and the intended usage. Just use a nice little boring bar.