I would like to see expansion test at those two speeds/respective bullets, same media......
I have little interest in hitting big game with a rifle bullet at 1300fps, just me. Now if we are talking a 45/70 bullet, ok, we already have good frontal diameter and great mass.
Several months ago (might have been over a year ago), when I first heard about the LR AB, I posted a question about the very issue you raise (expansion tests) in the Ask the Gunwriters/Experts forum, but nobody had a response at that time.
I personally can't see myself going down to a 1300 fps impact velocity either, but if expansion consistently occurs at 1600 fps, then you get more flexibility with mid-sized and small 6.5mm cartridges at "moderately long" ranges (e.g., 400-600 yds).
