A higher foc will basicly make the fletchings more efficient and tends to make the arrow more accurate at long ranges than an arrow with low FOC. If you have an arrow with an aluminum (light) insert adding on a heavy tip will generaly improve the arrows stability an make it more accurate. If your arrows have a brass insert (heavy) you can use a lighter tip and achieve the same thing. It also depends on the fletching...tall/long fletching will stabilize well even with a low FOC, but if you use say Blazers a higher tip weight will give the smaller vanes more leverage and they can steer the arrow as well as a larger fletching. You can use weight washers but they are only 5grs each so you will have to stack them to get the same weight, or change or add weight to the insert.
Wyvern