That's a broken 125MM barrel of a T-90A, Russia's currant top of the line tank
So after a frustrating day where nothing right happens, I finally got some time to settle down and get some more work done one my T-80BV. So I start with some PE. I get it off the fret and cleaned up no probs. Test positioning the piece it gets attacked the carpet monster. After a small battle lasting a few minutes I won. Settle down again getting some done the Carpet monster attacks again. After a half hour battle the monster wins this round and I fabricate a replacement part after about 10 minutes work. All PE in place an I realize Trumpeter's placement of parts while not 100% wrong is found on very few of my reference pics. So I remove all the PE, clean up surfaces and prepare to reposition more accurately. All parts except the last in place then the Carpet Monster attacks again. In a battle worthy of legends lasting over 2 hours it slays me, forcing me to replicate the PE part. Overall a rather irritating build session but still going with the kit and after a rather more successful time the next day no lasting damage.
All's well that ends well (even if its takes more work)