Crossbow Broadheads, Tuning For Superior Accuracy:
If you're using fixed blade broadheads out of a crossbow, tuning the broadhead is critical and while it may seem frustrating to do this, the rewards of doing so will be less time wasted looking for bad hit animals and more meat in the freezer.
A shorter crossbow arrow has less ability to stabilize in flight than a longer arrow.
Most crossbowmen will use mechanical heads as a shortcut instead of tuning their arrows. This is not an acceptable short cut to trying a number of fixed blade broadheads to see which ones fly the best.
Simply put mechanical heads waste 25 to 50 percent of an arrow's penetrating energy just to open up and crossbow arrows are light thus giving up much needed energy to effectively open a mechanical broadhead. The butterfly action of these heads plus their long noses combine to create high penetrating friction.
The other detracting factor to mechanical broadheads is, the blades are not supported at the rear when open and they can easily fold or snap on impact with bone or even heavy ribs. Our Extensive Crossbow Arrow Testing Made Light Of These Facts:
1. Anything less than 5" fletching length, on short crossbow arrows 15"-22" length, the arrows will not satisfactorily stabilize in flight, for excellent short and long range distance accuracy "period".
2. Penetration and accuracies went hand in hand by arrow length with well made three bladed broadheads as follows;
15"-18" arrows 7/8"-1" cutting diameter
18"-20" arrows 1"-1 1/16" cutting diameter
20"-22" arrows 1 1/16"-1 1/8" cutting diameter.
3. Alignment of the fletching and the blades resulted in an increase that was very measurable of accuracy at longer ranges or more distant targets.
4. Centrifugal force and run-out alignment test of arrows with broadheads and field points resulted in higher yields of pinpoint accuracy than the usual wobble test.
5. Front Of Center (ie; f.o.c.) arrow weight distribution for short crossbow arrows heavily favors 12.5% for superior accuracy and penetraion, at just 8% or 16% accuracy and flat trajectory flight falls off to the point it is noticable on distant targets including loss of penetration.
6. Of all the crossbow arrows and crossbow arrow manufacturers we tested, the new Beman ICS Carbon LightningBolt with ViBrake inserts required very little adjustment using quality 100 grain field points and quality 100 grain broadheads turning in excellent results with many different velocity crossbows.
7. Of all the broadheads and broadhead manufacturers in penetration tests and accuracy tests, the Trophy Ridge Ultimate Steel Broadheads performed almost to perfection.
8. By using quality; crossbow arrows and components thereof, we achieved extreme accuracy and tested up to a velocity of 340 feet per second with little effort and only minor problems stabilizing flight from 0 yards to 50 yards. Making The Adjustments:
#3 Aligning broadhead blades with the arrow fletching. There are several companies that make aluminum, steel, nylon and rubber washers or spacers that will allow you to align the fletching with a good three blade broadhead. These will also aid in setting your (F.O.C.) correctly by fine tuning your weight.
When looking down the arrow shaft from the nock end your three blade broadhead and fletching should look like the below diagram.
#4 The wobble test as it is known through out the world of archery is spinning the arrow in v-blocks to see if the broadhead is in true alignment with the arrow shaft and then visually make a judgement by eye only, whether it is concentric or not, to the best of my machining knowledge the human eye can not discern the difference of a few thousandths of an inch in measuring what is known as run-out.
 It is my belief that this is where most accuracy issues arise with bowhunters in tuning their broadheads.
The tool to the left is the RCBS Case Master gauging tool used in ammunition reloading, it is a very useful tool for tuning arrows as well.
By placing the arrow in the v-blocks you simply lower the run-out gauge down to make contact with broadhead ferrule where it is attached to the arrow, spin the arrow and observe the run out gauge for the run-out and make adjustments accordingly by loosening and retightening the broadhead until it is in perfect alignment with the arrow shaft.
Next for the centrifugal force test you will need a battery powered variable speed drill of good quality a v-notch cut in a board and a good steady hand.- 1st Along the arrow shaft find the balancing point and mark it with a marker of some kind DO NOT use tape.
- 2nd Chuck the nock end of the arrow into the drill, you can put a piece of tape here so as not to mark up your arrow and don't crush the nock either.
- 3rd Lay the arrow down into the notch of the board and slowly accelerate the drill until it is running at full speed, as you accelerate the drill if you notice the arrow start bouncing hard "stop the drill" and remove the arrow because it just failed the centrifugal force test, there is most likely something inside the arrow that you can not see that has it out of balance or it is bent.
#5 Adusting (F.O.C.) or "front of center" weight distribution of the assembled arrow with broadhead installed. There is no perfect F.O.C. for each individual arrow and broadhead setup.
However you can pretty well eliminate the old problem of trying to get your broaheads to impact the target in the same spot as your field tips just by selecting the same weight for each and the same length for each.
The reason for selecting same weight and same length is quite simple the oscillation in your arrow that you can not see is duplicated exactly the same for both field tip and broadhead.
The balance of an arrow can be modified by adding weight or reducing weight to the front of the arrow as needed.
In order for an arrow to fly correctly, the center of mass or (balance point) must be located somewhere between the tip and the middle of the arrow of its entire assembled length in other words its entire length from the tip of the broadhead to the end of the nock or center of its total (Over All Length).
If the center of mass or (balance point) is located close to the tip, the arrow will have good stability but will drop quicker and have less penetration because of the heavy nose.
If the center of mass or (balance point) is located close to the center of the shaft, the arrow will have good range and good penetraton, but arrow flight may be unstable.
Common F.O.C. for hunting and field archery is 10% - 15%. While this may not be an exact science to selecting a correct broadhead for hunting, there is a very exacting science to this and I will explain. It is all about the yardage, energy retention and flat trajectory! How To Calculate The F.O.C. Of An Arrow:
1st Measure the full length of your arrow from tip to nock and if you have been paying attention to all the above details in bold print your field points and broadheads will be the exact same length, write this number down. Divide this measurement by 2, this is the exact center of your arrow. Make a mark on your arrow.
(Example) 21 3/16" convert fraction to decimal divide the 16 into the 3 = .187 so the overall length is 21.187" now divide this by 2 = 10.593" place a small mark on your arrow at this measurement with a marker.
2nd Now balance your arrow on a pencil or whatever you have and measure from your balance point back to your mark that is center of your arrow. Now take this number and multiply by 100. Write this number down.
(Example) 2" x 100 = 200
3rd Now take your second number and divide by your arrows total over all length number = % F.O.C.
(Example) 200 divided by 21.187 = 9.439% F.O.C. Making Good Use Of F.O.C. Calculations:
In the above example you will see the F.O.C is out of the normal range for hunting, the balance weight is more toward the center of the arrow.
Now is this a bad thing? If you have accuracy at the normal hunting range that is well within your capability the answer is no, why, because that arrow will fly a flatter trajectory than the same arrow with a higher F.O.C., so how do you increase the F.O.C., if the arrow does not have good accuracy, you simply use a heavier broadhead to increase it. Why? As you bring the nose of the arrow down you will increase the accuracy, why, more air is forced onto the fletching which is the steering on the arrow, but you will start loosing your flat trajectory, why, because you are adding weight to the arrow thus a loss of velocity and your increasing drag by passing more air onto the fletching which decreases velocity as well. A Bad Current Trend In Bowhunting Concerning Broadheads:
It seems to me that in the world of bowhunting as of late, everyone is shooting large cut diameter expandable broadheads "bigger holes kill quicker", true, as long as that arrow exits the animal and leaves a blood trail so you can find it.
A 7/8" - 1" hole through the vitals of any animal alive on this planet will succumb to hemorrhaging as this is how an arrow kills effectively.
By using a smaller diameter cutting broadhead at lower velocities or higher velocities with lighter arrows you are pretty much guaranteed a pass through shot and have a good blood trail to follow to find your quarry.
By all means use as large a cutting diameter broadhead that your fletching will allow you as long as you know you will have a pass through shot on your quarry so you may find it. If You Have Not Gained Accuracy Yet:
These next three pages will certainly identify your crossbow accuracy problem, Broadhead Accuracy, Maintenance & Tuning and Accurate Scope Mounting. |
