Grains of arrow / feet per second

[Morning Star]

Just an idle curiosity.


Is there a generally accepted grain weight to feet per second correlation?

Example:

If I increased my arrow weight 25 grains, how many fps would I loose?  Or say, if I removed 25 grains how many fps would I gain?

Lets figure a bow around 50lbs @ 28", I realize a bows weight and draw length gives variables.

[R H Clark]

I don't think you could set a standard in fps.A lot would depend on how efficient the bow is.I don't think you could tell much difference with 25 grns on most bows.I would assume the margin of error on draw length and release would be nearly as great as the 25 grn difference.

[pdk25]

Agree with R H Clark.  Don't think 25 grains makes a big enough difference to worry about.  I also am pretty sure that you won't get a set change in fps for a given change in weight.  KE equals 1/2 mass times the velocity squared.  You can see it isn't a linear arrangement.  Increasing in weight should increase the efficiency of energy transfer, but i don't think you will get a good "thumbrule" to use.  I'm sure some of the physics experts will be along shortly.

[PV]

When I was playing with wheels 5 grains equaled 1 fps.Don't know if this correlates to trad bows.

[CJC]

imho 25 grains will make a fairly big difference in fps. for my setup its about 6 fps.that being said i am primarily a target shooter and every bit of speed is important to me.

[snag]

Just curious CJC. Why is "every bit of speed" important to a target shooter? I would think that if you know your bow are constant with your form and know the tradgetory of your arrow it wouldn't matter what speed the arrow is. It has to cover the same distance no matter if it is fast or a little slower...just wondering.

[zwickeyman]

Snag,

 It's just a matter of less margin for error because of flatter trajectory. With no concern of K.E. on a target as long as you are tuned and have a correct F.O.C. , the faster the better. I shoot 7.5gpp for target and 10gpp to 11gpp for hunting. I agree with PV and CJC, about 1 fps per 5 or 6 gr.
Zwickeyman

[Larry247]

25grns wouldn't make that much differance.

I could mix them in with some guys set ups and they'd never know the differance.

[James Wrenn]

Adding 25gns to a 300gn arrow is a lot different than adding 25grs to a 600gn or heavier arrow.With the heavy arrow it might not be noticed if in the middle of the spine range at all.With the 300gn you might would need to retune.It is all about percentages so there is no one answer that fits.

[Michl]

My 50#/27" widow speed increased 5fps when I changed from 450 to 425.

[Greg Skinner]

James is correct.  I saw no difference in either tuning or arrow speed whatsoever going from 700 to 725 with a 54# ELB.

[jrchambers]

i lost 20 fps going from 600 to 820, the change in fps decelerates the more wieght you get. for my setup.