The B-Square mt doesn't require any drilling or tapping as far as I know and is very solid.The caveman drilling for the rear screw in Weaver style mts shoots loose and doesn't leave much purchase for the screw either.Where was your #4 made and has it been altered? Two groove barrel or more? Longbranch [Canada] is one of the best along with Savage made guns. Overall bore size can vary between makers and wear and tear.I find scoping a .303 raises the cheek off the buttstock somewhat affecting comfort[hold] somewhat.Harold *same power as your US 30-40 Krag different bore size