What function do standard armor-piercing rounds serve(the ones that are a hard metal core[depleted uranium, steel, tungsten, etc] wrapped in lead and/or copper jacket)?

In game terms, there's no difference (as far as i know?). If anything, they just don't pierce armour as well. Just use APDS since it serves the same function, and really is basically the same thing.

If you really want to include them, just give them a price of 40 and AP -2

I've used AV ammunition for armour penetrators, because if they can shoot through vehicle armour, they should have no problem at all shooting through what you're wearing.

What you're describing here is AV, Arsenal p34.

Thanks! Didnt know that AV rounds are the "old style" APs

AV or APDS are both power-punchers.

Don't think about this too hard. Either your head will explode or you'll start rewriting large chunks of the rules.

Or, in extreme cases, both. It's not pretty.