I doubt the stones will help much but they have a hundred other useful purposes so your not out anything. And I could be wrong, maybe they'll work great. I was wrong once, I think it was 1962, maybe 63. Sad day that was.
Are you using a block to back up your sandpaper or just paper and fingers. I never sand without some sort of wood block. For stocks and grips I use a wood block with some thin felt wrapped around it. Had the same block for years.
The block of course helps keep the flats flat so there are no dips. Very important on the slide, relatively important on the frame too.
It's some times tough at the edges and uneven surfaces. I'm sure you know all this, the ones I've seen you do before looked perfect, no rounded corners etc.
Carry on.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."