October 28, 2010
The subject I'm going to be covering in this month's column -- Creep Testing -- is a little complex and a little lengthy but very important nonetheless. All that valuable information just wouldn't fit into one column, so it's going to be a two part article that will continue in the June issue.
As a bowhunter, you need to be very consistent with your draw length. You need to pull the bow back to the same place in the valley every time. The best way to do that with today's bows is to pull slightly (not hard) against the stops. The key to doing this well, as in all things related to shooting a bow, is to do it exactly the same way every time. Unfortunately, none of us are consistent enough to do it perfectly each time. The "Creep Test" will help you tune some forgiveness into your bow and compensate for those times when you pull too hard or not hard enough.
Back in my early days of field and indoor archery competition, most of the good shooters used what we called "round wheel" bows. These bows had small cams and smooth, rounded draw force curves. These bows were very forgiving and easy to tune and shoot. The problem was, they were also very slow.
We were instructed to draw these bows and hold them in the exact middle of the valley. However, it was difficult to determine just where the middle of the valley was, because the valley on these bows could be very long. I remember painting marks on my cables at eye level so I could line them up at full draw, making certain I maintained a consistent draw length for each shot.
In the early '80s, 3-D archery was becoming very popular and the competitors demanded faster bows to help minimize the effect of yardage judging mistakes.
One of the easiest ways to make a compound bow faster is to use an aggressive cam. The valleys on these bows became razor thin. In order to maximize the potential energy stored in the bow's limbs at full draw, draw force curves began to look more like a box than a bell curve. Unfortunately, these hard cams were much more prone to timing and synchronization issues.
As I spent more time shooting these bows, I began to notice that I would get high and low arrows for no apparent reason. My pin was on the spot, I executed the shot well, but my arrow would miss high or low. Most often, these misses occurred when I held the bow at full draw for a long time. And most often, the misses were high.
At that time, I had been competing long enough to know the difference between a good shot and a bad shot, and these misses were good, relaxed shots. But they weren't hitting where they were aimed. It took me a while, but I finally figured out that my misses were because I was creeping forward on some shots that I held too long and pulling too hard into the stops on others.
With some bows, allowing the arrow to move forward by as little as an eighth of an inch at full draw seemed to change the impact point significantly. This minor variation in draw length could cause me to miss by an inch or more at 20 yards. Now, that might not seem like much to a hunter, but it can be the difference between first and fifth place at a national tournament.
Now, up to this point, I had always timed my cams so the top cam and the bottom cam rolled over at exactly the same time as I came to full draw. I would then shoot through paper at six feet and tune the bow by adjusting the nocking point or the arrow rest until I got a perfect bullet hole through paper. However, as you'll see, I soon discovered that having the cams roll over at the exact same time did not always produce the most forgiving setup.
Well, I began to experiment with minor variations in cam synchronization. I was doing most of this fine-tuning by twisting one cable or the other to slightly alter its length, thus changing the individual cam's timing. Then, I would shoot one arrow pulling hard against the stops and then shoot another arrow creeped forward as much as possible. My goal was to get these two arrows to hit in the same spot. I called this the "Creep Test." I wanted to tune the high and low misses out of the bow. I found, on most bows, the creep test worked best when the top cam rolled over ever-so-slightly ahead of the bottom cam as the bow came to full draw.
So, you are probably asking, what practical application does this have to me, the average bowhunter? Well, if you haven't figured it out for yourself already, you are going to have to read next month's column, where we'll discuss the practical applications of the Creep Test for us bowhunters.