10 grains per pound is not correct

[sleek]

Badger, are you saying that all bows shoot better at 24 than at 28 with a 10 gpp arrow?  Seems to me a longer bow would fare better at 28, for example an elb.

[sleek]

Sleek, I think the 10 gpp figure is often cited so that at least one variable can be held constant when comparing the performance of two different bows. That is all the 10 gpp figure is for. No one is saying everyone should always shoot with arrows that weigh 10 gpp.

The method you are suggesting would effectively invite us to compare the performance of two different bows by holding nothing constant. What is the point of making the comparison, then?

Actually, in this equation 28 inches IS the constant. It allows all draw lengths to be compared to a 28 inch draw, regardless if draw weight and length. It is far from NOTHING being a constant. By deffinition,  the equation HAS a constant. I dont think you understand the math there and the point of my argument.

[Badger]

  Sleek, at 10 grains per pound the 28 inch draw has an advantage over the shorter draws but using the handicap the shorter draw bows would gain an advantage over the 28" draw bows. A very significant advanatge in some cases. Also shorter arrows seem to fly further.

[High-Desert]

Badger, what do you think the reasoning for your bow shooting after at 24"? Maybe you already explained it, but I missed it. It's very interesting. It does seem that there would be an optimum arrow weight for each individual bow based on tiller and profile.
I get what sleek is getting at, but it seems there are far more variables. You could tiller a bow to shoot light arrow for its poundage, or design to shoot heavy for its draw weight. How the bow is "geared". Isn't that like comparing a diesel truck to a dragster? Both have 700 horses, but neither can do the job of the other. Ignore me if I'm way off here.

[sleek]

I guess if my goal were to be to build a bow that shoots a 10 gpp arrow the fastest, id build a bow to that purpose, and take draw lenth into account. If thats the only goal. No complaints there.

If the goal is to put all bows in a level playing field, where midgets can run against giants in a fair equal foot race, the field needs to be adjusted accordingly. Then its a fair compareisin in all bows to eachother, and not to a specific purpose or task.

[Badger]

Badger, what do you think the reasoning for your bow shooting after at 24"? Maybe you already explained it, but I missed it. It's very interesting. It does seem that there would be an optimum arrow weight for each individual bow based on tiller and profile.
I get what sleek is getting at, but it seems there are far more variables. You could tiller a bow to shoot light arrow for its poundage, or design to shoot heavy for its draw weight. How the bow is "geared". Isn't that like comparing a diesel truck to a dragster? Both have 700 horses, but neither can do the job of the other. Ignore me if I'm way off here.

  In this case it wasn't gearing. It was simply the bow took on more set and hysteresis after being drawn out further. This will be true to some extent in nearly all bows. Hysteresis is a major loss in wood bows. The last few years around here I have seen a huge improvement in how well the bows are holding their profiles, I am also seeing a big jump in reported speeds these same bows are shooting. The bow I am talking about if I went back to drawing it at 24" would not have anywhere near the speed it had before being drawn out to 28". It was now a 28" draw bow and would be a dud at 24" from that point on.

[Eric Garza]

  I was going to give a real life example of a test that was done publicly. In 2008 we held a walk the talk event which was open to all kinds of bows both modern and primitive. I had a bow that was doing particularly well at home drawing 24" and I chose to leave it there to demonstrate short draw capabilities. At 24" draw and 10 grains per pound it was shooting at 175 fps. About the fastest I had ever gotten at 24". Using the Woodbear stored energy method shooting a 428 grain arrow it was hitting 186. When it came time for the formal test there were a lot of bows in line and it was too much trouble to readjust the shooting machine for 24" so I told them to just shoot the bow at 28" after a series of pulls to seat the bow in. At 28" and 10 grains per pound the bow was now shooting at 176 I believe. 9 fps below what the equivalent arrow weight was hitting at 24" draw.

That is fascinating. I am editing up our conversation for my podcast, and just listened to both of us talking about how we have been preferring longer bows as of late. Now you are making me want to revisit shorter bows and polish up my snap draw.

What were the dimensions of the bow you tested? Length, draw weight at 24 and 28 inches?

[Badger]

  Eric I had built 4 bows that were bamboo backed osage and almost twins. They went from 65 to 67" overall length and were reflex deflex designs in the low 50's. I think they were built with about 2 1/2" reflex. One was tillered to 24" one 26" and two at 28". One of the 28's broke during the test. I gave the 26" away without testing.

[Badger]

  i should have added that this bow was tillered for a shorter bending area than a 28" draw would need, a little luxury shorter draw bows can enjoy.

[Eric Garza]

So, for the sake of clarity, one of the 65-67 inch bows was tillered to 50 lbs at 24 inches, one was tillered to 50 @ 26, and two were tillered to 50 @ 28? So draw weight was constant at the different draw lengths?

[Badger]

So, for the sake of clarity, one of the 65-67 inch bows was tillered to 50 lbs at 24 inches, one was tillered to 50 @ 26, and two were tillered to 50 @ 28? So draw weight was constant at the different draw lengths?

, They were very close in the low 50's and were tested with corresponding arrows. The 24" I had tested more at home because I was intrigued with its short draw speed.

[DC]

5
 10gpp x draw/28

Can someone explain how to use this. What is the 5 doing up there?

[sleek]

Typo, fat fingers, small keyboard. Sorry.

[DC]

Thanks. I tend to short draw a bit so it looks like I should be shooting 9 gpp.

[Stick Bender]

I dont think there is a problem with the 10 gpp rule  its just one factor the problem with chrono numbers is they can easely be skewd most self bows will shoot 5-15 fps on average faster when fresh, I have done a lot of testing on that & posted ,and other guys here to , and leaving a bow strung for 1 hr & pre shooting a bow before testing even more loss , after about 300 arrows things seem to stabelise in my testing ,so my point is it would be dishonest for me to post fresh numbers that would do nobody any good especialy my self wanting to know what a design will really do in the real world I think hunters tend to want real world numbers setting in a stand or blind for hours can change a bow ! sinew  & laminate bows seem to be less effected by it in my testing ! Not scientific but practical tests.