Given that the Berger AR hybrid round has a G7 BC of 0.287, what would the BC be if the tip of the bullet were hardened steel? The steel has a lower density, so the BC would be lowered. If the bullet were of lead-free construction, like the M80A1, the BC might drop as low as 0.23 — for a design of about the same shape and size. But if it were backed by a lead slug, instead of a copper slug, The BC would be higher, perhaps as high as 0.25, but the weight would be lower, due to steel replacing some of the lead, weighing in at perhaps around 120 grains.
Such a design, a lead and steel EPR round in 6.5×50 ICS, could reach 2550 fps from a 14.5″ barrel. It would be effective at penetrating a wide range of barriers, and would certainly qualify as armor piercing. But with that velocity and BC, the round would have the following values at 800 meters:
drop: 8.7 mils
drift: 2.5 mils
velocity: 1233 fps (Mach 1.1)
energy: 405 ft-lbs
Those are excellent numbers for a modest recoil round and a 14″ barrel. This rifle and ammo combination would be effective in CQB as well as medium to long range combat. Muzzle energy is only 1740 ft-lbs, which implies very limited recoil, far less than the 7.62×51 NATO. And with a good muzzle device, the recoil would be no more than the 5.56 NATO round (with the birdcage flash hider).
But really, to obtain the most effective EPR, you need a lead slug behind the steel tip. The round will tumble better, and have a higher BC. And the extra weight behind the steel tip will help it penetrate barriers.
UPDATE: Okay, it turns out that such a round exists. Textron developed a lead-free 6.5mm EPR, including the hardened steel penetrator. G7 BC is about 0.246, based on their claims for muzzle velocity and for terminal energy at 1200 meters. So with a muzzle velocity of 2550 fps (1784 ft-lbs), the values at 800 meters are 1237 fps and 417 ft-lbs. Drop the muzzle velocity to 2450 and you get about the same values at 750 meters. Drop it again to 2350 and the same values appear at 700 meters. Recoil can be quite modest, if we are willing to give up 50 to 100 meters of range.