Why not something in 7.62x39, the preferred caliber of our enemies? I’ve owned one. Mild recoil and utter reliability. 308 is considered mid sized but it still packs large caliber recoil. That’s one of the reasons we got rid of it.
We need to be able to push bullets with heft (e.g., 150 grain) long distances over open spaces in Afghanistan. A .308, a very accurate round, is up to the task.