500 to 600 yds is done all day long with barrels starting @ 24 inches and longer! I have a 26" barrel that loves 155 & 190's, 10 twist.
I am not aware of a formula, but there are twist recommendations for all bullets! IMO, I believe a 12 twist will get the job done, 155's up to 190's, with at least a 26" barrel. I shot both, but I was using a 28" barrel.
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