with Dr. Mark Timney
Perfect Broadhead Flight
Many bowhunters have trouble making their broadheads group or hit where their field points do. This usually occurs because they're not paying attention to all the critical details that affect broadhead flight. You have to be certain of bow tune, provide enough fletch, watch front-of-center balance, and use straight arrows and components if you want your broadheads to fly true.
The Well-Tuned Bow?
This should go without saying... BUT... make sure you're using the proper arrow spine and that your bow is `in-tune.' I prefer to use computer programs to select my shafts as they're more accurate than charts and easier to use. I use Easton's "Shaft Selector Pro" program and one from Kentucky Flight Engineers called "Arrow Dynamics" (2KFE@GTE.NET). Both are easy to use, but the latter has a wider range of arrows to choose from.
Computer programs make choosing the right arrow a snap. Easton's program (on the left) is very simple to use. If you need or want more detailed information, look to "Arrow Dynamics" (on the right). The program provides a ton of useful information on arrows, bow dynamics and just about anything you need to know about the interaction between a bow and arrow.
Next, take the time to tune your bow perfectly. Don't be mislead into thinking you're in-tune because you can shoot tight groups with field points. Believe it or not, it's possible for a bow to be out-of-tune and shoot sub 1-inch groups at 20 yards with field points. Broadheads aren't as forgiving, especially if you're shooting over 260fps. This is because the blades on a broadhead can act as wings and `steer' an arrow, especially a poorly launched arrow.
There are hundreds of articles on bow-tuning, so I won't get into that here. But if you'd like to learn how to do it right, read Larry Wise's definitive book on the subject, "Tuning Your Compound Bow," from Target Communications.
While these drawings may look like chicken tracks to you, learning to paper-tune and `read' paper tears isn't that difficult. Here's a quick quiz: Which tear is showing a low nock point and a weak-acting spine for a right handed archer? The answer is at the bottom of the column.
Got Enough Fletch?
A good number of bowhunters are going for arrow speed by reducing arrow weight. That's okay, within reason, but don't save weight by cutting way back on the size of your fletch.
Arrows with field points can get by with very little fletch guidance. Not so for broadheads. You need a lot of fletch to counteract any attempt by the broadhead to steer your arrow. The general recommendation is that release shooters use 5" vanes or 4 or 5" feathers. I've found you can sometimes get away with 4" vanes and 3" feathers on arrows weighing less than 450-grains, but it never hurts to have a little extra guidance.
Finger shooters should always go with a 5" feather fletch. They need all the help they can get to counter the initial wobble of a finger-released arrow.... and that's true even if you have a very good release.
And whether you're using a release or fingers you should have a helical setting on your fletch. (Small diameter carbon shafts sometimes won't clear their rest with helical, but you can get almost always get away with an slight off-set.) You NEVER want a perfectly straight fletch when shooting broadheads. Fletches set in a helical do a much better job of stabilization. And, despite the `old wives tales,' feathers and a helical fletch will not slow your arrows down range. They are initially faster and only start losing a few FPS once you're well past typical hunting ranges (50 yards).
Feathers have advantages and disadvantages in comparison to vanes. They're nosier and they don't handle weather well, but they provide much more guidance. This is because they have a rougher surface which creates more air friction. I shoot 4" feathers on my compound setup and 4" feathers in a four-fletch configuration for my recurve.
Weighing in on `FOC'
A lot of bowhunters have trouble with broadheads because they're unaware of the front- of-center (FOC) balance point of their arrow. Very simply stated, FOC is the point on the arrow at which the fletch uses leverage to correct arrow flight. The further forward the FOC, the longer the `lever' the fletch has to work with and the easier its job.
The general FOC recommendation is 12 to 15% for broadheads (compared to 8-11% for field points). Finger shooters, and those shooting shafts less than 26-inches in length should lean toward the 15% figure. This is because shorter arrows are inherently less stable, and finger shooters, once again, need a little extra help to correct the normal arrow wobble upon release.
Do the math yourself. Here's how I do it... and since I'm no math wiz it's pretty simple. The formula is: [(ABP ÷ TAL) - .50] x100 = FOC. ABP is the measurement of the Arrow Balance Point for the tail of the arrow, and TAL is the Total Arrow Length.
All you need is a tape measure and something to balance an arrow on (like a pencil) to figure out your FOC. First, balance the arrow and mark where the balance point is. Then, measure the length of your arrow from where the string contacts the nock up to where the insert goes into the shaft. Next, measure from the throat of the nock to the mark you made at the balance
point. Finally, input the figures into the FOC formula- [(ABP ÷ TAL) - .50] x100 = FOC. For example: If you had a 30" arrow that balanced at 19" the formula would read [(19÷30) - .50] x 100 = 13.3% FOC.
If you find your arrow's FOC is too far back and you really don't want to change shafts or components, try switching to feathers. They're much lighter than vanes and should move your FOC forward by 2% or more. You can also use a lighter nock. I particularly like the `Tune-a-Nocks" from Quality Archery Designs (804-846-5839). They're super light, accurate, and they work especially well if you shoot a string loop like I do.
If your FOC is too far back you can either use a heavier broadhead (if your shaft spine can handle it), or lighten up the rear end of your arrow with feathers or lighter nocks.
Get it Straight
Always check to make sure your arrows are perfectly straight and that your components are in-line with the shaft. The easiest way I've found to do this is with a tool called "The Arrow Inspector" from Pine-Ridge Archery (email@example.com). One quick spin on the Arrow Inspector will reveal even the slightest bend.
This tool is also invaluable for mounting traditional heads as it helps you get the heads on perfectly straight. If you use replaceable broadheads, the tool will also point out if your insert/outsert is sitting straight. I've never had bent broadheads out of the package from my favorite manufacturers-- Magnus (www.bowsite.com/magnus) and Muzzy (www.gomuzzy.com)]-- but it never hurts to check every broadhead for straightness too.
You just set the arrow on the Arrow Inspector and spin it. If the shaft is bent it will come to a stop and then roll backwards a little. The device will also help you mount broadheads, check for crooked heads, and install inserts and outserts.
Getting your broadheads to fly true shouldn't be a study in frustration. Just follow the practical steps I've covered here and you should be set. But don't complain to me if you're soon cutting the fletches off your arrows because your broadheads are grouping so well! Good Hunting!
QUIZ ANSWER: Tear "B" shows an arrow that is acting weak and taking off from the bow with its tail low. You might be able to correct this by raising the nock point and moving the arrow rest to the left a little, but you also might end up needing a stiffer shaft.