at a SASS shoot last weekend I met a shooter that loads grits on top of his powder charge, he claims it takes up empty space and compresses the load(which I can see),but he also claims the grits scrub his barrel without doing any damage. anyone done this? is it going to cause any problems/damage?

Tis a common practice with reduced BP & BP substitute loads, them or cream of wheat. Just a filler. No cleaning effects I have ever seen.

I get my extra-scouring-power grits next to the spools of flight line and on the shelf above the 5-gallon buckets of prop-wash...

Seriously, it fills the empty space in the cartridge case and that's about it. I've seen cotton fiber used as a filler as well.

I have used fillers but stopped because after shooting a round I would look through the bore to see if anything stayed in it. if I missed the first shot the game I was after ran away while I was checking the bore.