Subject: Re: Let’s See If This Pans Out for Putin
Not mounted on tanks.

True. The T-90 has a 125 standard. I doubled-checked to be sure, but their tanks going back to at least the T-64 are all smooth-bore 125s. I didn't check older than the T-64.

Not 155. That's only NATO.

NATO tanks use 120 smooth bore (at least the Leopard and Abrams).