Wooden Self Bow Draw Weight Going Down and Up

Wooden Self Bow Draw Weight Going Down and Up

I’ve been playing around with draw weights and arrow speeds and differences. For a couple days I would take a bow and check the draw weight. Then shoot 12 arrows through it. The arrows are around 640gr. Each shot is through the chronograph and the hi, low and Ave recorded. I then check the draw weight again, shoot the 12 arrows, check the weight. (typically it’s considered best practice to drop the highest and lowest score, but my chrono doesn’t do that, so I just went with it as it was)

I found that each set I lost a little draw weight. The first set might be right around a pound. Maybe a little less for lighter bows. Each set looses a little less each time. After about 4 or 5 sets the weight loss stops. From then on it was consistent.

Cast drops slightly with the weight loss as would be expected. Total loss is never 4#, can come close for a 55# bow, and may only be a pound or two on a 40# bow. My osage board bow actually gained 4# the first time before going into the loss routine, and a Hophornbeam gained after a couple of days.  The HHB wasn’t completely shot in though.

The next day I would start over, all weight had been regained and a very similar routine starts. The end weight is close to yesterdays end weight but usually not the same (although this could be inconsistencies in weighing and my scale)

I’ve searched but could never find any references as to the draw weight going down, so I though if it was normal that seems odd I couldn’t find anyone noting it or asking, if it’s not normal how did I manage it on absolutely every bow I’ve made.

It’s turns out it is quite normal for a wood self bow.

It’s soft set. Wood compacts a little and then expands when rested.

I was concerned about using hickory which I have easy access to because I hear a lot of folks talk about how their hickory bow loosing weight even in a day of humid shooting. Wood reacting to moisture that quick didn’t make sense to me. Others say that as long as a bow is kept indoors and then taken for  a day or two of hunting in the rain will not matter if the bow is well protected, which makes perfect sense.

Now I believe what those folk who see the weight drop have is this “soft set” condition (which should have it’s own name I think) and has nothing to do with moisture content. 

For a hunting bow, it’s that first arrow that counts most of the time, so this whole thing doesn’t matter. However, for a target bow it’s required to know how the bow changes over time. It’s not as simple as a single draw weight. It would be wise to verify how many shots your bow needs to settle into a consistent weight and how it is affecting your arrow spine.

I confirmed this is not moisture related. Some of the bows have been in my shop for months and since it was raining during some of my testing, several of the test scenarios never left the shop and even going outside, moisture isn’t going to affect wood in the few minutes it take to shoot a dozen or even a few dozen arrows.
Here is the sample logs for the HHB bow, but I seen similar results on oak, maple, hickory, black walnut and osage bows. 

 

 

 

One comment

Leave a Reply