arrow weight per draw weight questions

[Josh B]

I had a chance to do a little playing around with a few bows and a chrono today and I got too wondering where the 10 gpp standard came from.  Is this just a convenient# to work with or perhaps an arbitrary # that someone just decided would be the standard?  I only had 3 bows and 3 weights of arrows with me at the time, so I was limited on the scope of experimentation.  All 3 bows are approximately60#@26" but all three were totally different designs.  My arrow weights were 350gr , 500 gr, and 600 gr.  Obviously the speed difference between the different arrow weights was quite significant.  But what got me to thinking about the gpp standard was the drop of the 600grainers compared to the 500 grainers with very little difference in penetration.  So I calculated the kinetic energy using the formula -arrow weight in oz.s x vel. Squared divided by 1029.12 = ft.lb.s of kinetic energy.  And then compared it with trajectory angles.  All 3 bows had a much better combination of flat trajectory and kinetic energy at 8Gpp than 10 gpp.  Any lighter arrow and the kinetic energy dropped drastically.  The heavier arrows dropped like a rock in there trajectory.  Any body else ever mess with this or ponder it?  Or do I just have too much time on my hands?  Obviously this was not a conclusive test, but it does have me curious.  Josh

[Badger]

  10 grains per pound is just a common arrow weight used for testing bows and preffered by many hunters as a good cross between speed and energy. KE always rises with arrow weight as does efficiency in the bow. 8 grains per pound is used by a lot of guys for it's flatter trajectory even though we have a slight loss in K.E.

[George Tsoukalas]

I shoot 9-11 gpp generally. Basically, the heavier the arrow the more it will absorb the energy transfer from the bow. That is physics. That is  why one feel less hand shock with a heavy arrow than a light one. So that 600 grain arrow would shoot nicely and probably just create a little thump. That 350 grain arrow does not enough mass to absorb the energy that your 60# bow wants to giver it, Gun Doc. Therefore, too much of the energy will be felt as limb vibration since it cannot go into the arrow. Remember that energy is never lost it is just transferred. It is transferred to us or to the arrow. To the arrow is better for us and the bow. The 10 gpp came about from experience... a compromise of sorts. It is a generalization. Some bows may shoot better with 12 gpp.  Selfbows have been around long before Sir Isaac Newton. LOL. Jawge

[crooketarrow]

  Unless your hunting 10 rings. With time as far as hunting go's you find out that it really dos'nt matter if you and your bow shoots it well. I use it of course I use make and shoot,shoot arrows where you'd have to go through 100 arrows to get a matched set.
  But I've found out long ago at 15 yards and the bucks in front of you. Hitting your spots much more important that what gpp your arrow is.  I've know people that thought they still had a compound in their hands. If one of there arrows is'nt the same they would'nt shoot it. Shooting a slow selfbow the gpp dos'nt matter. I can vision a couple indains setting around the camp fire decussing the gpp of their arrows. If it shoots out of your bow use it.
  If your looking for a basic reasons for ggp George perrty much said it all.
  As GOERGE said it came ABOUT about through exsperience.

[Josh B]

All valid points made.  I see a trend towards the mentioning of experience.  I'm not as 'seasoned'  as you fellows are, but I'm not exactly New to archery either.  What I am just now exploring is the high tech stuff like the internet, chronograph, precision scales and the like.  I've always made my arrows to fit the bow with the best combination of speed, penetration, and of course, as Jawge mentioned least hand shock(energy inefficiency).  I was completely oblivious to  any gpp standard until I got my first laptop and found this site.  I then got a hold of the TBB series and started to get interested in the more scientific aspects.  I'm sure this and many other questions I come up with are 'old hat' for a lot of you.  But for me, just being told that something just is, has never quite satisfied my curiosities.  I seem to always want to know 'why' it is. With my limited experiment, 8 gpp worked better.  Thus the questions.  Thanks for your replies, it's always good to hear from the masters and gain from that wealth of knowledge.  Josh

[JW_Halverson]

The largest buck I ever got with a bow* was killed with a 425 grain arrow out of a sinew backed osage bow with 50#'s of draw weight.  It was a very fast death as I got both lungs, he was down and stone cold dead in under 6 minutes.  Having said that, the handshock loosened fillings in my teeth and caused my toenails to fall out!  I got 156-158 fps from those arrows. 

Last year I took out some heavy ash arrows I had made and shot them thru the same bow.  Tamed the handshock wonderfully but dropped the arrow speed to 148 fps.    Obviously the bow design favored heavy arrows because I didn't lose all that much speed.  So I weighed them and was shocked to find they were just over 700 grains!

All in all, hitting that sweet spot with the arrow is the most important part, followed by hair splitting razor edges on the broadheads, and confidence in your bow for the third part.  10 gpp is a great place to start working from.

*the first buck, the only buck, and the best eating buck to boot!