The perk is added at the end of the rifle perk tree, to improve rifles in general for people who want to specialize in them rather than the other weapons. This would also work with Shotguns to be honest, you could very easily combine shotguns and rifles into a single tree called long guns
Hand loading. Careful attention to your ammunition has increased damage, penetration, and speed for all rifle cartridges.
This perk does for rifles and shotguns what pumping iron does for bows, and while it is a very end game perk it could answer a lot of people's issues with how the rifles actually work in CotW. Boosting the penetration and expansion of rifle rounds in a game friendly way that would make older/weaker weapons more effective for the people that like them over the bows and handguns