Well, here's my nerd moment for today:
The SRS99 Sniper rifle uses 14,5 x 114 APFSDS rounds, that's even bigger than 50cal, which is 12,7 x 99mm! It's potentially self sharpening trough armor penetration and could deliver incendiary and HE rounds or guided bullets as well.
So Jun is probably telling the truth here.
Only thing to trump this would be 20mm anti tank rifles...
Looks badass for sure!