Draw weight and FPS

[jeffp51]

All things being equal, How much FPS can be gained for each increased pound of draw weight?  On the one hand, if you stay at 10 grains/pound, then you perhaps keep the same arrow speed, but gain the ability to shoot a heavier arrow.  Is this right?

On the other hand, if you keep the same arrow weight, but up the draw weight, what will happen speed-wise?  It seems to me there are limitations both on how light you can make an arrow and how heavy you can make it. My heavier bows "feel" faster than my lighter bows, but I wonder if a well-made 35lb bow will ever shoot as fast as a well-made 65lb bow.

[bradsmith2010]

 

[jeffp51]

Yeah, Brad, I like to stir the pot now and then.  But I am not trying to bring up the old question about which is best for hunting.  That question seems pretty clear to me.  What I really want to know is if draw weight can increase arrow speed.

[Badger]

  You said all things being equal, if all things are equal heavier will always outshoot lighter. If they are not equal then it would just depend how slow the heavy one was and how fast the lighter one was. There is a big range of performance on these bows. If you are not talking equal weight arrows a lighter bow can easily outshoot a heavier bow with a lighter arrow both shooting 10 grains per pound. I have gotten as much as 300 fps with a 120 grain arrow but it was useless to shoot in flight as it was too light to cut through the air.

[jeffp51]

So let's just say I have a 50 pound bow that shoots 150fps.  A 55@ bow could probably shoot the same arrow without the spine or weight being too far off to lose accuracy.  How much faster would the heavier bow likely shoot the same arrow?

[PatM]

  You said all things being equal, if all things are equal heavier will always outshoot lighter. If they are not equal then it would just depend how slow the heavy one was and how fast the lighter one was. There is a big range of performance on these bows. If you are not talking equal weight arrows a lighter bow can easily outshoot a heavier bow with a lighter arrow both shooting 10 grains per pound. I have gotten as much as 300 fps with a 120 grain arrow but it was useless to shoot in flight as it was too light to cut through the air.

 How did Drake shoot over 500 with a 140 grain arrow?

[timmyd]

there is literally no way you could predict this. the only way that you could would be if the relationship between bow weight and FPS gain is a linear relationship and its not.

[Hawkdancer]

I think you may see a slight difference between a 50# & a 55#, but you would need a chronograph to tell.  35-65 should be appreciably noticeable, but still need the Chrono for hard data comparison.  There is probably very little difference in the spine.  Have to break out my new Chrono on the next nice day and exercise me and the bows,  i can test 45#,46#, and 50# bow with arrow weights varying between 520(?) and about 590 gr. 6 arrows each set. Might be fun.  May try it at an indoor range.
Hawkdancer

[willie]

So let's just say I have a 50 pound bow that shoots 150fps.  A 55@ bow could probably shoot the same arrow without the spine or weight being too far off to lose accuracy.  How much faster would the heavier bow likely shoot the same arrow?

here is a ez web calculator. try some trial and error combos to find equal kinetic energy

http://utopiaprogramming.com/ke/KineticEnergy.html#

[avcase]

How did Drake shoot over 500 with a 140 grain arrow?

Drake: shot over 1000 yards with about a 62 grain arrow!

These were shot with a flipper release and long overdraw, but it’s still ridiculously impressive.

Back on topic, my heavier bows are usually much more efficient with low ggp arrows than my lighter bows. It may not be as noticeable at 10ggp.


Alan

[JNystrom]

Back on topic, my heavier bows are usually much more efficient with low ggp arrows than my lighter bows. It may not be as noticeable at 10ggp.

This surprised me. Shouldn't it be exactly the opposite? Or do you mean for example 3gpp on 80 pound bow versus 40 pound bow. If both bows shoot same weight arrow, for example 150 grains, the lighter bow is more efficient, right?

[Badger]

So let's just say I have a 50 pound bow that shoots 150fps.  A 55@ bow could probably shoot the same arrow without the spine or weight being too far off to lose accuracy.  How much faster would the heavier bow likely shoot the same arrow?

   The speed likely would be between about 5 to 8 fps difference depending on the bow

[Stick Bender]

I think there is a sweet spot on any design where the extra mass needed to increase the draw weight negates the arrow speed ,I had a hickory bow increase speed at a lighter draw weight , cant prove it but been my exsperience. It seems all things cant be equal if your increasing mass 

[Eric Krewson]

I made a 70# hickory bow, third bow I think, poorly tillered, with boat paddle limbs and 1" tips. It had so much hand shock it would jar your toenails loose. My current 45# bow is much faster than that dog of a hickory bow I made.

It was rattlesnake skin backed and looked impressive. I gave it to a local guy who hosted archery clinics for children to use as a display model of a selfbow. No telling how many kids have seen that bow over the last 20 years.

[Springbuck]

So let's just say I have a 50 pound bow that shoots 150fps.  A 55@ bow could probably shoot the same arrow without the spine or weight being too far off to lose accuracy.  How much faster would the heavier bow likely shoot the same arrow?

   So I say yes,  the 55lb bow will shoot, like Badger said, several FPS faster, maybe as much as 10 fps, ASSUMING OF COURSE, that we didn't screw over the tiller, that we didn't add mass in a weird spot, that the 55 lb bow took no more set than the 50 lb bow, that nothing about the profile changed, that you can still pull the bow and not short draw it, etc...

  Sometimes you might gain that much in other ways, like heat treating in a little reflex and controlling tip weight.