10 of unique or 11 of herco will put you in the vacintity of 1000 fps give or take 50 fps. If you want more then that, which with a 250swc is a great whitetail load, id consider switching to 110, 2400, lilgun, aa9,4227 ect as the slower powders will get you that velocity without near the pressure. My favorite 44 mag load is 20-22 grains of h4227 with a mag primer and a 250 cast. Another would be 20 grains of aa9 and the same primer and bullet. Im not a big fan of 110 its a good top end powder but its just not very flexible. It cant be down loaded and its harder then most to ignite which is something a fellow michigander can appreciate especially if you walk outside right now as its 11 below zero on my thermometer. The best advise i can give you is to buy a loading manual. Theres alot of good SAFE loads for the .44s in them. Your taking a big chance taking advise on loading over the internet as you have no idea the experience level of the man giving it. Theres people that have loaded a hundred shells and think there the god appointed expert on loading and theres even idiots that give bad adivise intentionaly. BE CAREFULL