Of the two bullets you ask about, I would go with the Hornady Interlock.
However, if I may be permitted to add my two pennies worth, I would consider the180 gr. Nosler Partition for a .300 mag. Get your load worked up and them drop back about a grain and a half and work back up with the matching Sierra Pro-Hunter or maybe the Game King. I've done this with two rifles, a Winchester M70 in .270 Win. and another M70 in .300 Win. mag. The .270 will shoot the 150 gr. Sierra Game King and the 150 gr. Nosler Partition so closely together with the same powder charge that no change is necessary switching from one to the other. I get the same results with the .300 Mag, using the 200 gr. Speer Hot Core for the practice bullet and the 200 gr. Nosler Partition for the actual hunt.
If you plan on using 180 gr. bullets the Sierra PH and GK should work as practice for the hunt and then using the Nosler for game. I like the 200 gr. bullet for elk when I use the .300. I don't feel the 200 gr. bullet is a handicap as I took a nice fat juicy cow elk at a lasered 530 yards with the Speer bullet. I hadn't found and 200 gr. PT's as my LGS so had to go with the Speers. That far out at almost 2900 FPS they worked just fine.
Paul B.