Dude
I think ya probably reverting to .22 estimation of hold over/under thats why ya missing
.177 is so the best calibre for everything from from FT to rats licking peanut butter off a stick
I use 7.9 grain premiers for FT and HFT and now hunting
YEAH as some will say they over penetrate.... they drill a hole straight through the kill zone ... therefore the quarry is killed
They dont run away ,sometimes jump high , sometimes kick abit with nerves ... chemical reaction in blood
Stick with it man ,like ya already been advised ,practice practice practice
Get bigger bags than an Asda shopping trolley
Good luck
Steve