I just recently cleared some brush extending my range out to 100yds, but have been shooting at 80.
A few things: moving out from 50yds I found that 75gr of 777 is a better load for my T/C Hawken shooting PRB.
I've also been pracicing w/ both eyes open; although this makes target aquisition seem easier, aiming this way brings eye fatigue quickly for me.
Once I dialed in the 75gr off a rest, a 40lb bag of wood pellets incidentally, most of my shots have been offhand both seated & standing. I'm finding that though I'm easily within a pie plate, bulls-eyes are not forthcoming.
I'll say this about offhand though it has already been touched on, the heft of the rifle has alot to do with accuracy at longer ranges.
I will admit, at 100 yds through iron sights the target seems a bit abstract to me. This is one reason I really enjoy archery as shots are 30 yds and under, at least for me, and you KNOW what you are looking at without a doubt as far as shot placement.