When I was doing some gunsmithing, and measured a lot of bores, I found great consistency of bore size within brands, but some variation between brands. Belgian made Brownings nearly always had 0.725" bores, most others were 0.730", except for Remington 1100 and 870 guns which were all over the place, mostly larger than 0.730". I actually found one 100 skeet barrel that measured 0.745" from the factory. I did a lot of screw-in chokes in single barrel guns, and the reamer and tap for the chokes came with 5 bushings from 0.730" down, and I had to buy blank bushings and turn them to size for the Remington barrels.