I'm thinking 20 km/s or higher....(?)
--Boris?
Or an APFSDS sabot round for their 2A42 30mm gun used on the BMP2 and BMP-3 Mech Infantry vehicles like the 25mm sabot rounds we have for the Bradley's Chain Gun, with performance somewhere between that of the US 25mm and the 30mm GAU-8 tank-killing Gatling Gun of the A10 *Warthog*.
There's a shoulder-fired 23mm Russian antitank rifle, too, a semirecoilless weapon something like an oversized M82A1 Barrett .50 caliber AMR. Maybe a really high performance round like the .50 Raufoos shaped charge has been developed for it, or maybe a light tripod-mounted 30mm version has been worked up....
I don't think we're quite to the point where a usable rail gun could be fielded in a package any smaller than roughly a 40-foot semitrailer truck or container, though it's certainly going to happen in the near future. But whether an electromagnetically accelerated projectile, a hypervelocity kinetic energy round, or an advanced small caliber chemical energy HEAT warhead, it's bad news for the crews in the Abrams...and worse news for those in Strykers.
-archy-/-
Back of the envelope, when you add up all the generators and capacitors needed to provide the electrical whallop needed, I'd say you are about right. The capacitors alone could weight thousands of pounds. I have done some VERY powerful strobe photography (did you know you can photograph nuclear explosions in their very early stages?) and the caps I used rolled on large carts, about the size of chest freezers but MUCH heavier.
I'm with you, I'm guessing that it was one of those .50 caliber sniper rifles with a new tech anti-armor round... There was some concern recently that Iran had acquired (illegally) some high performance .50 cal sniper rifles. Alternatively Iran has made a 12.7 anti material weapon which, as some posts suggest may be being field tested see:
http://forums.military.com/groupee/forums/a/tpc/f/2741923366/m/1600037510001