The carbine is shooting high because of the increased recoil of the heavy bullet. The lighter gun has more muzzle rise.
Actually, neither load is shooting high or low, they just have a different POI compared to the same POA. Adjust your sights for the heavy load in a carbine and the light stuff will have a lower POI.
wow, I found just the opposite with my M44 Russain.
I had it sighted in for the 147 gr Albanian lb.
When I shot the 203 gr. Barnaul SP,
I was hitting 10" lower @100 yds.
I figured I'd better test with the ammo I would be hunting with.
Glad I did.