He is FOS. Even if his rifle could shoot 1/4" groups at 100yds, that would equate to 6.25" groups at 2500yds assuming absolutly no wind or shooter error. Have him shoot a 1/2" group at 500yds if he gives you any crap about not having a 2500yd range to show you on.
My high-end AR in .308 (POF) shot this at 300 yds, a 1" or under group plus a "flyer" bringing it out to about +1.5." If it wasn't for shooter error, I bet it could do 1/3 MOA at 300 yards. I am working on that.
I consider that pretty outrageous accuracy from semi with factory ammo. Much better than 1/4 MOA, and I am very skeptical.
Army maximum effective range of 308 is 800 meters, Marines say 1000 meters, record is 1200 in combat. All well short of the claimed 2500 yards. Money in the bank!