Saw a reddit post about wanting a model with striations for their teacher. Grabbed a model from gradCAD, quick sketch, sweep and you have some striations. The punched primer is also tapered and at an angle but due to it's size, it is not easy to tell.

Dimensions of the striations depth is a guess. They are tapered and have a slight rotation. The bullet and cartridge have an added .15mm clearance to hopefully press fit.

Scale to suit the desired purpose. The larger the model, the better the striation/punch will show. The model's size is that of a true 5.5x45NATO round.

Remix of https://grabcad.com/library/bullet-5-56x45mm-nato-1 GrabCAD and Makerworld don't want to talk to eachother so I can't upload as a remix.