Kinetic energy---- got my eyes opened!!

[Blacky]

Laurent,

I just checked your graphs and must say: nice work. As you may know I'm doing a lot of reviews for various magazines and my testing guidlines are also very strict.

Looking at your graphs I could see the following:

ACS: total weight difference is 300 grains, speed loss/gain is 45 fps = appr. 6,7 grains for 1 fps.

Fedora: total weight difference is 300 grains, speed loss/gain is 41 fps = appr. 7,3 grains for 1 fps.

Black Widow: total weight difference is 300 grains, speed loss/gain is 49 fps = appr. 6,1 grains for 1 fps.

RER: total weight difference is 300 grains, speed loss/gain is 42 fps = appr. 7,2 grains for 1 fps.

I'm testing my bows with 6 to 10 gpp, so my findings are different, especially with foam core limbs. I used part of your charts and looked at the lighter arrow weights. If I take the part between 550 grains and 400 grains I see the following:

ACS: total weight difference is 150 grains, speed loss/gain is 26 fps = appr. 5,7 grains for 1 fps.

Fedora: total weight difference is 150 grains, speed loss/gain is 22 fps = appr. 6,8 grains for 1 fps.

BW: total weight difference is 150 grains, speed loss/gain is 25 fps = appr. 6 grains for 1 fps.

RER: total weight difference is 150 grains, speed loss/gain is 22 fps = appr. 6,8 grains for 1 fps.

If you go towards 6 gpp you'll get close to 3 - 5 grains for a speed difference of 1 fps, especially with ILF limbs. This thread shouldn't end as a pi$$ing contest, but you can see that my numbers even match your charts. I never tested bows over 11 gpp, so you have the edge in this department. When I do quick calculations, I use 4 to 5 grains for 1 fps, which ever is easier to calculate.

Blacky

[hybridbow hunter]

Sure they are !  
ours test bows are done in a wide range of arrow weight in ready to hunt conditions with a random bow from the company while magazine test is done only at 9 gpp and with a naked string with a bow send to the tester in the purpose of magazine review      

[hybridbow hunter]

Blacky
I know your work and respect it.
My assesment was 10 gr variation leads to 1 to 1,5 fps variation in hunting bows. So 100 gr leads to 10 to 15 fps.
So 300 gr lead to 30 to 45 fps variation right? that what show the graphs. Bur these 300 gr on bows in the 50# range represent 6 unit in gpp variation. If you take a 60#+ bow, variation on those 300 gr will be on 5 or less unit of gpp, thus the "loss of speed" will go down , closer to the 100 gr/ 10 fps.

If you look to  average "hunting arrow weight" thus 500 to 650 gr  the variation is right on 150 gr/ more or less 20 fps and if you look close to the 10 to 12 gpp range (wich is the sweet spot for dynamic efficiency)  those 100 gr go for less than 15 fps in speed variation at least for 3 of the bows.
if i put the graphs for light R/D  LB or straight LB in the 10 to 13 gpp  you will go more for 100 gr/ 10 fps speed variation.

Our testing protocol is more orientate towards hunting, maybe that is why our result are a bit different.
Glad to share some bow physics with you.
Regards

[Ragnarok Forge]

Guys thanks for the posts.   I love technical info.  Both methods were just shown to be valid and that they correlate well.  I have noticed during personal experimentation that 10 fps makes little difference in point of impact @ 20 yards.  30 yards is a different story.   This info will help put a lot of speculation to rest.   Blacky,  it must be nice to have all the latest bows to test and shoot on a regular basis.  Lots of folks here would love to have that opportunity.

[chopx2]

Man I wish my release and accuracy were good enough to notice the difference.
   

 :D

[wildgame]

Originally posted by MCNSC:
I learned this the hard way. If you are happy with your bow don't shoot it thru a chrono.      

X 2

[BrokenArrows]

This stuff'll make ya crazy!?

Know a guy w an ACS longbow. Most tests I see those are 200 fps at 9 gpp. He gets 180 fps. Is the diff him, the bow, string, arrows, or chrony? Beats me.  

IMO, a lot of variation in a lot of fingers out there is dragging some stuff down. And funky cronys.

Sometimes I see what Blacky sees (50g = 10 fps), and sometimes I see the other (50g = 5 fps).

I have a bow that does one w a Dacron string and the other w a Fast Flight Plus string...

I just don't think this stuff is as repeatable w bows, strings, and arrows as it is w guns and ammo. Fingers on a string make way more difference than fingers on a trigger. Way more variation in the former than the latter IMO.