I was reading through a 1940's vintage reloading manual written by Philip Sharpe, the Complete Guide to Handloading.
In it, he talks about sizing bullets, and he cited an experiment whereby bullets were loaded and fired as much as .006-.008 overbore. His conclusion was that they shot fine with zero accuracy or pressure problems, and that as long as bullets are sized at least .001-002 larger than the bore, then they are fine to use.
Given this, why bother with slugging your bore looking for that exact .001-.002 overbore measurement? I recently loaded some .45-70 rounds into my 1886 Browning, which I'd previously slugged to be about .458. The boolits I loaded came out at .463-.464. I loaded and fired them, and noticed absolutely nothing but tight groups (better than the .460's I'd been using!)
So I'm asking, why not simply use a boolit several thou larger than bore diameter and forget about slugging for the "perfect" bullet size? If it's too large, the act of firing it swages it down to the right size anyway, doesn't it?