By Randy Ulmer
Because I only get a few shots a year at big-game animals - and I've usually got a month or more invested in scouting the particular animal I'm shooting at I am extremely particular about my arrows. I've chosen my current hunting arrow based on a lot of years of tournament competition and many more years of bowhunting experience.
There are several qualities essential in good hunting arrows: straightness; uniform spine (along the length as well as around the shaft); a well-aligned broadhead; consistent weight; a strong, well-fitting nock; and perfect fletching. However, in my opinion, one of the most important characteristics of a hunting arrow, especially here in the West where I do the vast majority of my hunting, is a micro-diameter shaft.
In this column, I'm going to do my best to talk you into shooting skinny arrows no matter where you hunt. I'll list all the reasons why I think you should be shooting micro-diameter arrows and discuss my thoughts on each aspect.
In all the testing I'm aware of, micro-diameter arrows have penetrated better than larger-diameter arrows of the same weight. Micro-diameter shafts tend to be all carbon or aluminum/carbon composite. Though the stiffness of the carbon does play a small role, shaft diameter appears to be the most important factor when it comes to penetration. A micro-diameter carbon shaft has a surface area approximately half that of larger-diameter shafts. The smaller surface area of the thin shaft vastly reduces the resistance (friction) as the arrow slips into the target.
Reduced Wind Drift
Today's narrowest carbon hunting arrows are very skinny compared to aluminum arrows or standard-diameter carbon shafts. Again, a micro-diameter carbon shaft has roughly half the surface area of standard shafts. Just as in penetration, wind drift is proportional to the total surface area of the arrow. When you shoot micro-diameter arrows in a crosswind, they exhibit much less sideways drift than larger-diameter arrows of the same weight.
Wind drift is usually of more concern to Western hunters than it is to Eastern hunters. However, I've spent many windy days in treestands while hunting Midwestern states. A micro-diameter arrow is more likely to hit the vitals than a fat shaft if you forget to compensate for the wind. By switching to small-diameter arrows with smaller fletching, you can cut your wind drift by more than half on longer shots.
Because many facets of hunting arrow performance are directly related to the surface area of the arrow, the surface area of the fletching must also be taken into account when determining how much total surface area the arrow has. Ideally, the less surface area the better as long as you can control the broadhead!
It takes much less fletching to start a micro-diameter shaft spinning than it does to start a large-diameter shaft spinning. This is because the mass of a large-diameter shaft is further away from its axis. Look at a figure skater to see what I mean. When their arms are straight out at the beginning of their spin, they rotate slowly. As they move their arms up and towards the center of their axis they spin much faster. So, you can use small fletching on small-diameter shafts. This further decreases the arrow's total surface area.
You can also use much smaller fletching if you choose a mechanical broadhead rather than a fixed-blade head. This is based on simple physics. The more turbulence you create on the front of the arrow, the more steering you will need on the back end of the arrow to get the same stabilization and accuracy. Using a very streamlined broadhead with little turbulence-producing structure will allow you to use much smaller fletching. I've found that if I use short fletching with maximum offset, I can reduce the surface area of the fletching (and arrow) while still maintaining the same control I would get using a larger fletching applied with less offset. Applying the vanes with a helical clamp seems to help as well. You can get significantly more offset (in degrees) with a short vane than with a long vane.
An added benefit of short, low-profile fletching is it decreases the noise the arrow makes as it flies through the air.
Better Downrange Velocity
Micro-diameter arrows also maintain their speed better downrange. Arrows slow down as they move forward because of the friction of the air they are passing through. The greater the surface area of an arrow, the quicker it slows down. Because skinny arrows maintain more of their speed, they also have more kinetic energy and better penetration at longer distances.
At 60 yards, small-diameter arrows lose a lower percentage of their initial velocity than a larger-diameter arrow. I know from my own experience that the difference between large-diameter and small-diameter arrows grows even greater at longer ranges. It may not be a huge difference, but bowhunting is a tough game and I'll take every advantage I can get!