Since max load is ~ 25gr, I'd go with the smaller increment - thus starting 10% below max is a super simple workup. Since it's lighter than published maximum, I'll offer that my Remingtons and Mossberg both shot hlf inch grps with 25gr TAC under 50Zs and that was my std .223 load for 5 years. One Remington still shot 1" grps (sufficient to hit most p-dogs out to 300yds) after 14,000 of these loads.
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