This mod removes many of the requirements for handmade rifle modifications, and adds 5.56 receivers that match all the pre-existing receivers. This allows you to effectively use any legendary handmades you find in the Commonwealth before starting Nuka-World, or use a mod that adds the handmade to Commonwealth levelled lists but don't also have a mod that adds DLC ammo. Though in that case, I really don't understand what you're doing.

Extract the .esp from this zip folder and enable in whatever mod manager you use.