I have a Leupold Mark 4 LR/T, 3.5-10X, M2 ILLUMINATED TMR. The top of it indicates the BDC is scribed for 7.62 168 gr. I haven't owned a rifle in .308 for about 30 years, but this winter I plan to buy a rifle to mount this scope on. One of the factory "Tactical's" of one brand or another. I don't intend to handload, but rather try to get the most out of the factory ammo available. I won't be hunting, or shooting competitively, just using it for trigger time and keeping the mileage off my hunting guns. So my question comes down to What barrel length 18-24", with which ammo brand will track "best" with this scope. I'm not expecting perfect, just close is fine.