30-378

I have a friend that has a 30-378 McMillan Rifle with a 30" inch barrel. The rate of twist is 1/10. The action is bedded and the barrel is free floated from the lug to the tip. He hand loads his ammo and is running a velocity of 3200-3300 fps. He is using a 180 grain bullet and cannot get better than a 3" group at a 100yrds. I suggested a 200 or a 225 grain bullet and backing down of the fps. I'm not sure of the powder but he said that he has the slowest burning powder he could find. He has 113 grains of powder with a slight compressed load.. My question for all those who are smarter than me is ..... What would you recommend he do with the situation...