I am trying to find 3 or 4 of the best factory loaded ammo for my 300wsm. as I am not set up to reload at this time. I have been using ballistic calculators to help narrow my search. I have been using 165gr. Fusions for the past 3 seasons with good success. My ballistic data was obtained without using tables or calculators but by shooting only and it has proven time and again to be very accurate in both drop and drift. The problem is when I take my proven data and plug it into a calculator everything is way off. Fusion says that bullet has a b.c. of .453 but for me to be able to match the calculated drop to my actual drop I have to drop the b.c. to around .320 and I can't get the drift to match no matter what I do. I have tried for many hours and made sure all the data I am entering into the calculators is accurate including the enviornmental parameters. If I can't take known data and make it work on a calculator how can I trust the given data when shopping for new ammo? It would take me years to buy,shoot, and compare all the different choices out there. I believe the problem to be my lack of experience with calculators because those of you who know how to use them swear by them. If someone can help shed some light this way cuz I'm having trouble seeing!