A newb question here. I may give competition a try in the near future. Handloading my own ammo is not feasible at this point in time. I see that Federal Gold Medal 223 Sierra Matchking comes in two weights: 69-gr and 77-gr. It isn't cheap ammo, so I'd rather not have to buy both (to compare), if I don't have to. Which is best for my rifle (see pic for specs)?