OK planning a build on either a brit #4 series action or a 1916 P14 action. Basically the 37 rimmed is a 303 Brit case necked up to 375 caliber. And no other changes, there is a tiny shoulder which basically does nothing. I reaching out to others who may have done a similar build maybe one of the various 375 cartridges. The barrel is a Douglas blank with 1x14 twist. Bullet weights 250-300 grains weight. So my question at this time how did you rework those two tabs at the ofront on the magazine?. Even with the 303 cartridge there is a fine line messing with the two tabs. Too high and they hit the bolt and too low won't feed cartridges. I'll get what parts which is basically everything below the bottom of the receiver.None of the items I need will not match either the bolt or receiver. All I have at the present is the action body and bolt. Liberty tree has the parts needed. Thanks,Frank