motivation for doing so would be that I could carry 7.62x25 ammo that's known for its penetration ability without the corrosive powder behind it. That and plus the only surplus on the market right now is polish and it isn't loaded as hot as the others...
It's NOT the powder that's corrosive, it's the primer compound,(the stuff that makes it able to start the powder burning.
If by bi-metal you mean common FMJ military ball ammo, then it's what you get when you order pulled military bullets. Most are copper plated steel jacketed , lead core bullets.
Armour piercing bullets are usually copper plated steel jacketed, with a hardened steel core, there may be some lead as well.
Is your main objective to defeat bullet proof vests?