I'm running the .97 on my sightron 56mm (65mm OD) OBJ. MTU contour. 2.55mm from bell to barrel. If I had went with the .92, I would only have 1.275mm from B to B. The .87 would set me on my barrel.
I forgot to mention. Remington 700, 20 moa leupold base. I'm hoping to get as close as possible without touching. Thanks for the info so far, keep it coming.