Intel6, are you using the stock barrel on the G20? Or a longer barrel?
As for 10mm ammo, there are two distinct power levels on the market. Full velocity stuff and .40S&W level stuff.
ProLoad, Triton, CorBon, Federal (155gr), Winchester, Hornady and Georgia Arms to name a few, load the 10mm in the hotter realms.
Beware of the Black Talon, Starfire and Hydra-Shok 10mms. . . I have seen butterflies beat these 10mm loadings down range!
Derek