At this point there are several things to do. Apply Dencorub to the shgoulder to prevent a bruise forming. Heparin also works but it spreads the bruise. Consider getting one of those plastic shoulder pads that the shotgunners use and sewing it into your uniform. Remove the shooting victim from the field using a period stretcher.
Nothing looks farbier than a gurney bouncing over a poughed field.
When in doubt - drag. Remove the outer clothing near the wound carefully. Prop up the victim carefully on a pile of newspapers. Remove the ball carefully with a pair of long-nose pliers. They can't do forensic tests on it if they can't find it.