Honestly, with cast, thinking splody like, hollow points, 18-2k. I don't have anywhere near the experience with those. Have taken several deer with the mp311-159hp, they work splendid. Giving up trajectory, harder to find entry/blow up balance.
I'm not to surprised it wants a little different combo. It's a different creature, just in the same cal. To chamber cast & do so well, first go round is a sign of fun to come. Way to go psa & Ian!
If you ran quickload on just the barrel length difference, it might explain most of it. That don't account for the other differences.
Couple guesses, 35-37gr 4895, rx7 25-31gr, 19-21 4227. I've worked varget backward in the carbine but haven't yet located the notes for minimum function.