Carpetsahib, if you have the time, could you please post a top view of your reworked #4?. I'd very much like to see what the top of the receiver looks like. I'm currently doing something like yours. I've a #4MKI receiver, 375 barrel with 1x12 twist, and a box full of never fired IVI 303 brass. So any help you could give will be greatly appreciated. I can't hunt anymore but like to make my own cast bullets and like the 375/303 cartridge. Hopefully will be able to do my own barrel work as this is a first for me. Thanks,Frank