IMR4350 is a very slow powder for 240-grain bullets in the large .444 case. The pressure was very low, the reason for the low velocity. Unburned powder is due to to the low pressures. This powder is designed for pressures above 45,000 cup and doesn't burn well much below that. The slowest powder that IMR lists for the 240-grain bullet in the .444 is IMR4895. For a moderate load use a faster powder, or accept the mess from the unburned IMR4350. It doesn't hurt anything as long as it does not gum up the action.