I do think caliber has a lot to do with accuracy in the #1. Like Ruger 4570 says, thickness and stiffness of the barrel, related to bore size and cartridge intensity, seems an important factor. My hunting pard has owned, and we have shot extensively: #!B in .270 Win. Average 1-1/2"-2" accuracy, with best groups from 150 grain bullets loaded to moderate levels; 1A .45-70: superb sub inch accuracy with full-load 350gr bullets; #1B in 6mm Remington, only shot near MOA with light bullets at moderate velocity; and finally my superb first year #1A .222, which can group as tightly as you can hold...the shooter is the deciding factor with this rifle.
I conclude barrel harmonics, low to medium intensity rounds, is a key factor. We could probably have achieved better results with extensive load testing. Who has the patience for that when he just wants to go hunting?
