Join Date: Jan 2010
Location: South Central Wisconsin, USA
A 1:12 .30cal twist will be fine for at least 170gr. bullets and still be fine with lighter. The common 1:10 of a 30-06 is good for heavier bullets and a throwback to the early days of the US Mil 30 cal 'requirements';ie, the 30-40 Krag with a 220. In truth the 1:12 makes a better all rounder for 30's unless yu actually 'need' to shoot those long, heavies for really big game.
I have not checked my Mustang 30-30 twist as it throws whatever I have fed it just fine.
What I think you are experiencing is the rising bullet effect, each bullet weight has a different trajectory and to have your, say, +/- 1" 'point blank'. Sight it in for the midrange of your given bullet to optimize the low/high for your requirements. Sighting in for -0- up close is a good start, and you can guestimate/calc the 100 yd but there is no substitute for real world, on the paper at 100.
FWIW, Id try for +1 at 75-100 then see where it prints at 50 and 125-150 just to know.
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