Hardcore rewards first-shot lethality, so the loadout question is rarely "what hits hardest." It is "what hits cleanest, every time, while I move." Three principles cover most of it.
Consistency over peak damage
One life means a single bad spray ends your round. Pick the option that behaves the same in every fight over the one with a flashier ceiling and a worse floor.
Mobility is information
Speed lets you take and break angles, which is how you gather and deny information. A slightly weaker gun you can reposition with often beats a stronger one that pins you in place.
The best attachment is the one that lets you leave a fight you are losing.
Do not build around a crutch
If your kit only works because of one item that the league might restrict, you have a fragile loadout. Build something that still functions when the meta shifts under you.
Restrictions are enforced live and change between seasons. Check the rulebook before a match. League guidelines →