I was just wondering about the ballistics charts (muzzle energy, muzzle velocity and bullet drop out ot 500 yards) that the various bullet manufacturers put on their web sites and on their ammo boxes.

Does anyone know the standard that the industry uses re barrel length and i guess it would be thickness to come up with these charts they advertise.

JUst curious because i was looking at the ballistics for the .308, .270 and .270 wsm and in the 2 or 3 different rifles i am considering buying the barrel length varies between 21.5 up to 24.5 and in between also consisting of sporter barrels (which i would believe to be lighter weight)

Also i would assume that the longer heavier barrel (eg; varmint rifle) would get the best ballistics.

Thanks.