There are two 300 grain .452 XTP bullets; the 300 grain XTP with two cannelures and the 300 grain XTP magnum bullet with one cannelure. Given the high retained weight, the bullet used in the OP is likely the 300 grain .452 magnum bullet.

The magnum bullet is another ball game; it's very tough. i've used both bullets on large hogs. There is also a 300 grain .430 XTP bullet with two cannelures.

http://www.hornady.com/store/XTP-XTP-MAG/?page=4