Triple Seven(777) is more potent than regular BP, Pyrodex or other well known substitutes by about 15%.
You should reduce your charge by 15% when using 777 measuring by volume.
I don't shoot BP handguns but if your charge is 36grns. of reg BP then you should use a charge of 30.6grns of 777.
If you used an actual measurement of 36grns. of 777 it would be the same as shooting 41.7grns of reg. BP, Pyrodex or most other subs.
Far as compression goes, again, speaking in long rifles, I run the projectile down till it is fully, but lightly seated.