I am late for the party, but here is a load that has worked for me on chucks. It absolutely blows them in half if shot in the body. It is a 75 grain Hornady HP at 3350 using 47 grains of 4350 powder. One grain above and one grain below, and it shoots an inch. With this load, I have shot many 200 yard groups less than 3/4" with a HB Sako 243. My favorite longer range chuck gun.
