A average mature/big bull has a 200" main frame. Deduct 10" for main beam length, 8" for width and around 7" for him being light on his mass and that's a 175" main frame. 45" main beams, 32" wide and 26.5" of mass per side.
10" G1
13" G2
8" G3
12" G4
7" G5
This puts him at 275"
No way that bull will make 300", He will be a very nice bull in a couple of years though. Depending on the area I was hunting I may let him walk, he defiantly wouldn't be a bull I would plan a hunt around.