Another thing, that i've SEEN happen is, ammo fired in HOT weather, the powder makes more pressure (pressure = fps) and so shoots slightly flatter. Shoot the same ammo in very cold weather and the V is slower!!

I've seen this many times with 22lr ammo, when winter hunting in cold weather high in the mountains for ptarmigan!!!

Anyway, magnus theory or not, i'm sticking with, bullets start to fall from the time they leave the bbl, and keep on falling!!!

Drilling Man