The newer 580 series are all 1:9 twist. Mine has stabilized 75gr. out to 100yrds. but I reload mainly 69gr for accuracy shooting. My best group is 1.25'' and I was shooting 60gr. sierra varmiter reloads. I dont know how well the 75gr would do past 100yrds. I have good luck with the 69gr so I will just stick with them.
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