I meant any cartridge period, production or experimental
Well with that qualifyer- I guess the U.S. Navy has to be in the running for top spot. Seems a couple of years ago they built some kind of electro-magnet propelled rail gun that squoze out a projectile at 8270fps or thereabouts.
I remember reading that it had like 40 feet of penetration ability. Now, I don't know what that 40' was that they were wanting to penetrate, just the number stuck.