As most shooters probably know, the lightest solid bullet which can be shot accurately in a rifled barrel is a round ball, and if they are truely round and fit, it is hard to beat their accuracy, because they are in balance no matter which way they turn. But they do not wound well when shot at big bore airgun speeds. This because tissue isn't splashed violently enough sidways to rip flesh and create a wound channel that causes rapid bleeding.
'subsonic' and I have discussed a plan for his 50, and very soon he should have a bullet that is a little heavier than a round ball, but with a substantial meplat, which will increase killing power dramatically. Watch for his posts about it.
Veral at LBT