Enlarging A Reamed Hole

I've used that trick on smaller holes if I didn't have access to (or time to make) a barrel lap. A cigarette rolling paper works well.

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This is an old toolmakers trick, very well known in the UK. You can also grind a drill to cut oversize.
 
Shimming a reamer is not unheard of. Brass and soft steel work best, and don't really show mark from reamer. The flutes of a reamer don't so much cut along the length, only the first small portion. Their action is more burnishing of tool marks. They taper away [less] from the tip.
Normally the shim is cut resembling a iso-triangle. The point, inserted between a pair of flutes holds it in place, the shape allows a gradual increase of diameter without collapsing shim or jamming in hole. Get results by steady feed rate, as the uncovered corner edges produce something like boring.
 
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