Congrats! I used 2 different rifles in 257 WBY ( just saying its fast for its caliber size) first was a converted Mod 700 25-06 (24"bbl) and I used the then available Federal Premium Nosler 115pt. Clocked them at 3200 and they worked swell too. A few years later, I bought a custom Mark X with 26" bbl and I handloaded the then new Barnes 100 TSX, close to 3500fps. Pure poison. I used the 180 Accubond going 3500fps from a 25" 338 RUM on a big Aoudad. They made an identical wound/exit hole as Partitions! So Monos, Partitions or Monos would be "my pick". I am "intrigued" by the 6.5/300 ever since I read about it in a Sierra Load manual of 1979! Let us know how the thing shoots pard? It has got to be a zinger! ha Have a ball too!