I learned this by modifying fmj 8mm ammo as a kid. The side cutter deformed bullets shot as well as the carefully filed ones.
My .358 Win shot so good with .358" boolits there was no reason to deviate. The same for my 30-30 bolt action except I use .309"- I tried .311" and went running back to .309". Slugging the bore is important because it is information- whether you use it or not is up to you.
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