While making sure your minimum weight is met you must also make sure your FOC (front of Center) balance is around 12%. If your FOC is to far back the arrow will fly erratic and if the FOC is to far forward your arrow will loose trajectory very quickly. To find the FOC: balance the arrow and measure from that point to the center. Take that number divided by the total length and you have your number.
Example 20" arrow with a balance point that is 2.4" front of center. 2.4/20= .12 or 12%.
Cross bow arrows as we will call them are made up of 5 Basic Parts
1. The Shaft: just as with compound bow arrows these shafts can be aluminum or carbon. Common sizes of arrows are 18, 20, 22". When buying arrows you will notice that they all show how much weight they are per inch this is very important for total weight.
2. The Nock: The Nock on a crossbow arrow comes in two basic varieties. Flat and Half Moon Shaped. As with compound bows you can also get these in lighted form.
3. The Vanes: Like all arrows these arrows have vanes of a variety of sizes and colors. Special attention should be given that the vanes are not to tall for use in your crossbow. The cock feather must ride down in the crossbow without bottoming out in the channel for the vane.
4. The Insert: This can be the biggest difference between a compound bow arrow and a cross bow arrow. In order to achieve desired weight or FOC (Front of Center) there are brass inserts that can range from around 20 up to around 110 grains.
5.The Head or Point: Broadhead companies are making broadheads specifically made for crossbows weighing up to 150 grains are common. The same head you shoot out of your compound could very well work on your cross bow setup as well. The lighter heads will more then likely require a heavier insert to keep the FOC correct and the total weight up to where it needs to be. Getting heavier inserts rather then different broad heads can mean only keeping one set of broad heads for both your compound bow and your crossbow.