Main Discussion Area > Arrows
10 gpp?
upstatenybowyer:
Forgive me friends, but I'm really trying to wrap my head around this "matching arrows to bows" thing.
Where does the 10 gpp guideline come from?
I'm wondering cause while waiting for my grain scale to arrive, and having a brand new chronograph to play with, I decided to shoot an arrow whose weight I know for sure through the chrony. That arrow was an aluminum alloy arrow that weighs 320 grains (I know cause I looked it up on the maker's site).
I shot the arrow with a 60# hackberry static and the speed was a little over 180 every time. I was getting low 170s with the same bow when shooting a cedar shaft arrow that I know was heavier.
My question is why do we go with 10 gpp as a guideline if a lighter arrow goes faster? Is the guideline specific to wood arrows? Is it a hunting/penetration thing?
Thanks for baring with me. (W
DC:
It's probably as simple as 10 is an easy number to remember :D I really doubt that there is a solid reason.
Pat B:
It is an ideal set up for a hunting arrow. Target arrows would be lighter.
Nidhoggr:
This will be lengthy:
A lighter arrow travels much faster but the trade off is it has less kinetic energy transfer and less momentum. So while it will travel further with height drop over distance, it will also not deliver as much force upon impact.
A heavier arrow will have much more kinetic force and more momentum, but the trade off is less speed and more of an arrow drop.
See this example here (albeit using carbon arrows and a compound, but same concept). If I recall correctly this is using a 60 lb compound as the example:
Weight Speed Kinetic Energy Momentum
350 gr. 340 fps 89.75 ft. lbs. .527 Slug/ft. per. sec
480 gr. 290 fps 89.54 ft. lbs. .617 Slug/ft. per. sec
750 gr. 175 fps 50.95 ft. lbs. .582 Slug/ft. per. sec
Notice the 750gr arrow has a much lower speed than the 350gr and the 480gr, but it's still got a higher energy? That's due to the GPP in relation to the poundage. The 480gr arrow is roughly in line with the 10gpp range. Notice it's kinetic energy is actually LESS than the 350gr arrow, but because of it's increased mass it is substantially more powerful when momentum comes into play. Not only that it has a pretty hefty speed vs the 750gr and not much less speed than the 350gr.
So essentially what it boils down to is 10 GPP is from a physics standpoint where the energy transfer is balanced well between weight that the poundage of the bow used can propel without sacrificing stability of shot, structural integrity of the arrow, or making the arrow too fast with less than ideal kinetic energy and momentum.
TLDR: 10 GPP is the sweet spot for an arrow achieving ideal performance and not just a random number lol.
DC:
That's way better than my answer :D
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