At 1000 yards, with the same 200-yard sight-in and 5 mph crosswind, the 129 started at 2900 goes like this:
Drop: -336
Drift: 52
Remaining velocity: 1226
These numbers, by the way, are all calculated at the standard elevation, temperature, etc. that ammo factories and loading manuals use for their ballistics charts.
While I have used both rounds a LONG ways out there on varmints, on big game my longest shots have been around 400 yards, both on pronghorn. I have also taken several big deer with both rounds, using a variety of bullets. The results are identical: If the bulet goes in the right place, the animal is dead very quickly.
I have never seen a big bull elk taken with either round, but have seen enough meat elk taken that I have no doubts that either would work--though I tend to prefer just a little more cartridge for such work. I do know a woman who has aken 17 elk with the .257 Roberts, with 17 shots. All were cows or meat bulls, and none were taken past 250 yards, but it worked just fine.
Right now I have two .257's and one 6.5x55, though the .257's are both factory rifles and the 6.5x55 a complete custom job on an FN action, with nice English-walnut stock, Lilja barrel, Gentry 3-position safety and Timney trigger. All shoot very well.
