Why don’t my broadheads hit where my field points do?
As hunting seasons approach, our attention turns from target shooting to bowhunting. We need to decide if we are going to use the same setup as last year or make some changes. It’s time to replace field points with broadheads. For me, this means fixed blade broadheads. We live in Oregon where it’s illegal to use mechanical broadheads on big game animals.
Because the broadhead’s blades act like miniature wings, any variation from a true straight delivery of the arrow causes the broadhead to steer away from a straight path, which causes the blades to catch even more air which in turn causes the arrow to steer even farther from the desired straight path.
We found out a long time ago, that not testing the broadhead tipped arrows we intended to hunt with was stupid. In the past, we’ve had as much as a two-foot difference (at 20 yds) between the field points and the broadheads impact points. The broadheads themselves, can vary from arrow to arrow such that it is sometimes difficult to have six arrows that are able to hit a paper plate at 20 yds.
Probably the biggest factor affecting broadhead flight is how the arrow is being delivered by the bow. Different bows can shoot the same broadhead tipped arrow and get different results. Even though the arrows are straight and the broadheads are straight with the shaft, the bow with the straightest nock travel always groups better.
A bow with straight up and down nock travel will probably still have left and right nock travel, which will affect the way a broadhead is delivered. Because the blades act like miniature wings, any variation from a true straight delivery of the arrow tends to cause the broadhead to steer away from a straight path, which causes the blades to catch even more air which in turn causes the arrow to steer even farther from the desired straight path.
We can minimize the effect the blades have on the arrow by causing the arrow to spin as it flies. Having large helical fletches on the arrows does a wonderful job of overcoming the steering effects of the blades on the broadhead, after it leaves the bow.
We have found that the reason why a broadhead tipped arrow will not hit the same place as a field point tipped arrow is because the arrow is not being delivered straight by the bow. Many bow manufacturers claim to have bows with “straight nock travel”. But do not be fooled. They are only talking about up & down nock travel. (Our slow motion camera shows that straight up & down nock travel only happens when using a loop-on-the-string.) There is also a left and right movement of the nock that the manufacturers don’t want to tell us about.
The bottom line is, no matter what bow you have the arrow is probably not being delivered “perfectly straight”. This means that before the arrow exits the bow, the blades of the broadhead are catching air and steering the arrow before the fletch can be of any help. The steering effect of the broadheads causes the arrows to be delivered differently than arrows with field points.
The orientation of the blades with respect to how the arrow is being delivered determines how much air the blades will catch. To get consistent grouping with fixed blade broadheads, each broadhead has to catch the same amount of air.
If the broadheads are perfectly true to the shaft and the blades of each broadhead on each arrow have the same orientation, the arrows should group quite nicely. It doesn’t really matter what the orientation is, as long as it’s consistent from arrow to arrow. There is a good chance that a particular orientation will be more forgiving. The closer we can get our broadheads to hit where our field tips hit, makes our setup more forgiving for shooting errors. Unfortunately, the blade orientation that works best on one bow may not be the best for a different bow.
The amount of air a broadhead catches also depends on blade size and the actual amount of blade surface that is available to catch the air. Smaller and vented blades have less surface available to catch air and tend to be more forgiving. Three bladed broadheads are the overall best when it comes to being forgiving and easiest for the fletch to keep straight because the 120 degree spacing between the blades minimizes the amount of steering.
Often times because of the broadhead steering effect, adjustments in the location of the arrow rest can offset the steering effects and result in better grouping due to an increase in forgiveness. (This is one reason we like micro-adjustable arrow-rests so much.)
Bows that store a lot of energy generally have a lot of left and right nock travel, and using an arrow rest that will provide side support can make a world of difference. Otherwise, a fall-away rest is hard to beat.
We’ve had problems getting the broadheads to be square with the arrow. Sometimes the end of threaded insert that the broadhead screws into was not square with the shaft. We made a gizmo so we could square the ends of the threaded inserts with a file after they were glued into the shafts. (No…we do not have any of those for sale. But, somebody else is marketing a gizmo just for that purpose. We haven’t used it so we don’t know how well it works.) We found that squaring the end of a problem arrow a lot of times fixed the arrow.
When we started using carbon arrows for hunting, we had a problem with getting the blades on the broadheads to be oriented the same on each arrow. We had used epoxy glue to install the threaded inserts and the only way we could change the orientation of the broadheads was to use the gizmo we had made for squaring the end of the insert and file off more material. It worked OK but was a real pain.
We can change the orientation on our aluminum arrows and that’s really nice. To change the orientation of the broadhead, all you have to do is heat up the shaft until the glue melts. This is a definite advantage. We like to use big broadheads that make big holes and if we get a chance to use our laser rangefinders, we like to be able to shoot long yardages. (We are better shots than we are hunters. Not that we are bad hunters.) Sometimes just a small change in how the broadhead is oriented can be used to offset variations in arrow straightness and broadhead alignment. By tweaking the orientation of the broadheads it is possible to bring a paper plate size grouping at 60 yards down to a grouping the size of a softball.
Because the Ferr-L-Tite heat melt glue is so handy, we did a big no-no and tried it in the carbon arrows. At first it did not work well at all. Since, you can’t heat the shaft up with a torch, we would screw a field point into the insert and then heat up the field point until the glue would melt. Then with the glue melted, the insert was pushed into the end of the shaft. (This has worked well for us on ACC’s.) We ruined the ends of about nine arrows before we got the feel for what was too hot and what was not hot enough. Fortunately, we had left the arrows long enough that we could trim the ruined portion off. (We found that you want to get the point just hot enough to melt the glue, if you get it too hot it warps the end of the arrow.)
So by watching how the glue melted we could gauge how hot the insert was and we installed the inserts in a dozen carbon arrows. We were pretty proud of ourselves until we started shooting the arrows and the inserts started coming out.
So we removed the inserts by heating up the point until the glue melted and trimmed ends off. Then we used a 7 mm brass gun cleaning brush to rough up the inside of the shaft. After cleaning the points and the inside of the shaft with a q-tip soaked in alcohol (or acetone), we glued the inserts back in with the heat melt glue. That worked pretty well but we were still losing an insert in the target every once and a while.
So we removed the inserts again. We melted some extra glue on the insert and scraped the extra melted glue to the inside of shaft. Now when we pushed the insert into the shaft there was some glue there that was re-melted by the hot insert and pushed ahead of the insert. By rotating the insert as it was pushed into the shaft that extra glue coated the inside of the shaft and now we don’t have any problems losing inserts.
If we want to reorient a broadhead we generally don’t heat up the broadhead because the torch can ruin the blades. We take the broadhead out and replace it with a field point that we heat up just enough to cause the glue to melt, then we rotate the insert.
By Steve Johnson