My 1250yard attempt

[LRRPF52]

I did some calculations on bullet weights a while back, and found interesting results. I found that a 129+ gr bullet was so heavy, that it never really got up to speed; and a 123 gr bullet actually was better for 1000 yards (the limit of the calculation comparisons), than a 129 was, because of this. The 123 would stay supersonic to 1000 yards, and would stay above 1000 ft-lb of energy for a longer distance than a 129 did; as the 129's just never were able to get up to speed in a Grendel in a 20" BBL. Which is to say, effective range and for both target and game usage, got longer as weight increased; until I hit 123 gr, after which it peaked and started coming back down. But that was all calculation, and for shorter 1000 yards usage. And of course can vary depending on specific bullet and how hard one pushes it. For your 1250 yard real-world experiment, I'm not sure - maybe that's too far for the 123 to reach after-all. Neat to see your usage and experiments.

I look at wind drift more than anything, followed by energy.

Even with a .260 Rem in 10-17mph fluctuating conditions, your hit probability drops down more to 800yds if the wind is that variable.