Its interesting that you are almost 10% less capacity. I wonder what affect its having on pressure.
If you weigh the 77gr bullets it doesn't say 79gr by any chance
What cases are they? Thick brass?
Lots of places on the net I can see people using 24gr with col ~2.260/5 and no one mentions compressed loads.
Are you using the regular SMKs (9377) or the tipped version (7177) which are slightly longer so the same col will push the bullet back in the case.
I'd like to try the 90s or the 95s
but need a 1:6.5 twist. Time to get a Valkyrie