I use 80gr Bergers through a 1/7 twist, and it's great at that distance. But I suspect that a 69gr. will be about the limit for your slower 1/9 twist. Maybe you could get away with 77gr, but I doubt it. The 80 & 90 grain bullets specifically say "for 1/8 or faster twist". Your 68 or 69 grainers will group OK, but you'll have to learn the wind calls. AFAIK, all the 600 yard CMP guys are shooting 69's as it the max they can get to fit magazine length, and some of those boys score really well.
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