Re: O.A.L for a DPMS LR 308
Yes, Just go with max mag length in your situation. Rifle reloading is much more forgiving than semi-auto handgun loads with COL adjustments, as it relates to pressure. I still would stay below max a bit & use a powder compatible with your semi-auto action. The medium/faster burners like H-4895 & TAC may work out well.
Make sure you are resized properly so you don't stick a case in your action.