Lots of 308 AR pins are "proprietary", in that each manufacturer uses their own diameter. Stag uses 0.277, DPMS uses 0.278, Knight's Armament uses 0.280. Some happen to match. Since there is no military specification, measure before you build.
The Stag 10 is *almost* an SR-25 (slant cut receiver, 1 7/16"-16 barrel nut thread), except for the pin diameter.
Fortunately, swapping out triggers and forends for the Stag 10 is not tricky. Get DPMS-high rails. 308 ARs use standard AR15 triggers; I have a Geissele High Speed National Match trigger in my Stag 10, for example.