The handload is Virgin Winchester brass that I plucked from the bag, primed, filled with 4350 and seated an 87 Vmax to kiss my Tikka. It may be a little long for the Cooper, fair enough. Different rifle, different chamber.
Just never heard of a factory rifle that won't take factory ammo. While Cooper may be on the higher end of the spectrum, I'd still expect it to take factory fodder.
