Tuning your crossbow bolts will help you tighten your groupings and will ultimately be a key part of your success.
To optimize your accuracy you need to understand what affects your crossbow bolts flight. The front of center of F.O.C. of your bolt can have a big influence on accuracy especially at longer ranges.
So what exactly is F.O.C.
F.O.C. describes the percentage of your crossbow bolt’s total weight that which is located in the front half of the bolt. The more weight that is located in the front half of the crossbow bolt, the more forward is the crossbow bolt’s center-of-balance.
The F.O.C. balance position of the crossbow bolt is one of the more important elements affecting the shape of the crossbow bolt’s trajectory curve. Ideal F.O.C is especially critical for target shooters participating in long-range shooting competitions or hunters that are pushing the their crossbows to the maximum shooting range.
While F.O.C is less relevant in some crossbow hunting situations (short-range shots), it can be critical in those long-range situations or if your shooting a crossbow with a low FPS rating. A high F.O.C. will fly with good stability, but will shed its trajectory quicker and nose-dive. While a crossbow bolt with low F.O.C. will hold its trajectory better, but can fly erratically. For hunting situations crossbow bolts with 10-15% F.O.C. for hunting setups and optimal accuracy.
How do I Find my F.O.C.?
First you need to begin by calculating the F.O.C. on your current bolt combination. To determine the F.O.C of a hunting crossbow bolt, install all the components you will be using on the shaft (points/broadheads, vanes, inserts, nock, etc.). Once your crossbow bolt is set up:
- Divide the crossbow bolt’s overall length (distance to the bottom of nock groove to end of shaft by 2).
- Find the balance point. This is where the crossbow bolt balances perfectly. Mark the point, and measure from the throat of the nock.
- Subtract center of the crossbow bolt measurement (calculated in step 1) from the balance point (calculated in step 2).
- Multiply the resulting number in Step 3 by 100.
- Divide the resulting number from Step 4 by the crossbow bolt’s overall length. This number is the F.O.C. of your hunting crossbow bolt.
If you find your hunting crossbow bolt’s F.O.C. to be exceptionally deviant from the recommended range of 10-15%, consider adding/removing weight to/from the front or rear of the crossbow bolt.
Tuning Crossbow Bolt F.O.C.
Adding weight to either the front or the rear of the shaft can modify the balance of an crossbow bolt. Heavier vanes, for example, increase the weight of the rear portion of the crossbow bolt (decreases the F.O.C.). Replacing vanes with feathers lightens the rear of the crossbow bolt. Heavier points, inserts, and even added weights are used to modify the weight of the front of the crossbow bolt (increases the F.O.C).