Most accurate is a Remington XP-100R, in 7mm-08, from the custom shop. It will shoot 1 1/2" groups at 200 yards.
Second most accurate is S&W .460 from their custom shop. It will shoot an inch at 100 yards
3rd most accurate Anschutz Exemplar in .22 LR. 3/8" groups at 50 yards.
I put a rifle scope on one of my Marvel 1 conversions, and found a couple of different types of ammo that would group under an inch at 75 yards.
I would rate my Les Baer Premier II, with the 1 1/2" @ 50 yard group guarantee even with my Sig Allround.