Dang now I have to say something
Normally I'd say the Abrams would outperform the Russian tank (which I believe is a T-90), but because the barrel is essentially non-existent, the Abrams won't have nearly as good shell velocity, accuracy, or penetration because the gases can't push the shell as much as they would be able to in a longer barrel. I'm not sure exactly how the guns would compare with the other tank's armor, but my guess is that that T-90 would win.