Basic weapon attachments should cost zero attachments points

Why does regular standard ammo cost 5 points? Only the next level so penetration ammo should cost 5 points, polymer 10 etc.

Why does the lowest magazine capacity/slowest reload attachment cost 5 points? It should be 0.

Why does iron sight cost 5 points? It should be 0.

Why the basic standard barrel usually costs like 10 points? It should be 0.

Optional the default parts could also be for free, but that could lead to too much balancing issues.