Was it already sighted in with that combo? If it was then make sure your scope is tight. If this a new load then as already mentioned, adjust you powder first. I found 150 gns of 777 with a 250 gn sabot works well, but each gun is different. Here's a punch list I swear by. Order of importance 1st
1. Swab the barrel between each shot. You hunt with a clean barrel so sight it in with a clean barrel.
2. Adjust powder loads up or down to get consistant placement at 50 yards, then adjust you scope to center. If your shots are not consistant you may have to try a different bullet.
3. After your shots are landing good at 50, stretch that to 100 and re-adjust.
A couple of hints. I marked my ramrods with a little
tractor paint (fingernail polish) at the spot where everything is seated. A quick glance when reloading and I know it's all tight. Also, a little spit on the sabot makes it push down the barrel a bit easier.
Hope this helps. And remember..............Aim small, shoot small.