Arrow speed Consistency limb-to-limb

[SJP51]

I have three Bob Lee Bows. Actually two handles and 3 limb sets. All 19" handles and 60" AMO. Same string material and strand count. Fine bows. Not complaining. Just observing.

The 57#, 47#, and 38# don't all produce the same arrow speed even though I have arrows at the same 9.0 gpp for each set up. There is a 7 fps spread, with the slowest being the 38# limbs.

Why is that?

[PYBUCK]

Physics, you answered your own question. The poundage of the limbs=arrowspeed.

[SJP51]

Physics, you answered your own question. The poundage of the limbs=arrowspeed.

But I've used the same GPP on all 3 arrows. So the 57# limbs are pushing a much heavier arrow than the 38# limbs.

[tvc184]

But I've used the same GPP on all 3 arrows. So the 57# limbs are pushing a much heavier arrow than the 38# limbs.

It is because of the efficiency of the limbs.

Get several different brands and models of bows and set them to the exact same poundage. Then shoot the same arrow through each.

Since you’re using the exact same poundage of bows and the same arrow (so the exact same GPP), they should be identical, correct? It should not matter the brand or which model, the GPP is still identical. What the GPP does not take into account is limb efficiency.

[SJP51]

It is because of the efficiency of the limbs.

Get several different brands and models of bows and set them to the exact same poundage. Then shoot the same arrow through each.

Since you’re using the exact same poundage of bows and the same arrow (so the exact same GPP), they should be identical, correct? It should not matter the brand or which model, the GPP is still identical. What the GPP does not take into account is limb efficiency.

Makes sense. I was assuming 3 sets of limbs from same maker would be same or very similar design (efficiency). Perhaps not!

[Fishndude]

Could be your machine. Could be your form. Could be what’s stated above. Could be arrows. Could be field tips. Could be vanes. Could be tune.

Thing is… now you know.

[Bisch]

Arrow speed Consistency limb-to-limb

Well, they are similar. 7fps over a 19# spread is really not all that big of a difference. You also have to remember, these are wood and glass limbs glued together. If there is any difference in the limb sets, i.e. difference in limb design (amount of hook in recurve limb, etc), different veneer wood, or a tiny amount of glue difference, or even just the fact that the veneers are different thicknesses can contribute to a gap as small as 7fps.

Now, if you had said there was a 27fps difference, I would think that something was out of whack!

And why didn’t you post this in the trad forum??? You might have actually got a bowyer who has a better, more accurate answer to reply there.

Bisch


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[tvc184]

Makes sense. I was assuming 3 sets of limbs from same maker would be same or very similar design (efficiency). Perhaps not!

I am just guessing (several years ago after talking to a person in an archery shop that sets up bows) that limb responses can be different. Did he know what he was talking about? I have no clue,. I took physics in high school but I sure don’t know what formulas use for limb efficiency. I doubt that he did either however he set up a lot of bows. This is what I asked him at the time.

If I buy a 50 to 60 pound bow or a 60 to 70 pound bow in the exact same model, would they shoot the same when both were set at 60 pounds. He said in his experience, no. With 50 to 60 pound limbs, setting it to 60 pounds was reaching its limit in other words it’s tension. Taking a 60 to 70 pounds set of limbs and setting to the low end of 60 pounds, it was less tension compared to the maximum of that limb set even though both were 60 pounds.

What he told me was that in his experience of setting up many bows, he got a couple of more feet per second out of the 50 to 60 limbs set at 60 as opposed to the 60 to 70 limbs set at 60. So in his experience, a 60 pound set bow of the exact same brand but with different limbs would not get the same speed on the same arrow. Is that true? I don’t know but it kind of makes sense to me.

[critter69]

Shoot you could shoot the same bow, arrow through the chrono time after time and get 7 fps difference. 7 FPS ES is actually really good even in firearms.

[DRT]

Did you actually put the bow with each limb set one scale and see if they scale what they are marked or just go with what the limb has written on it?

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[Bisch]

Did you actually put the bow with each limb set one scale and see if they scale what they are marked or just go with what the limb has written on it?

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Did not think of that^^^^^^, but it is an excellent point as well!!!!!

Bisch


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[SJP51]

Did you actually put the bow with each limb set one scale and see if they scale what they are marked or just go with what the limb has written on it?

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All the limbs are spec'd @28" and I draw 29". Did scale the 47# and th 38#, but not the 57#. Good thought as I was "assuming" they'd be 59# at 29". I might give that some time this afternoon and double check the other two while I'm at it. But some hammock time is calling.

Another thing is that the two handles are not "excatly" the same. Slight variance in sight window height since Bob Lee's are hand made and not pushed out a factory door like the ILF risers.

This whole thing was an attempt to see if all 3 sets of limbs would shoot the same velocity and produce the same arrow drop, so I could shoot the same hold 20 yards. And, of course, and excuse to play with my toys!

Too many variables. I think this whole effort was futile!

[SJP51]

Shoot you could shoot the same bow, arrow through the chrono time after time and get 7 fps difference. 7 FPS ES is actually really good even in firearms.

And here I was hoping to get +/- 2 fps! Not sure my old chrono is even that repeatable at the low end of its scale.

[RedYote]

Even at recurve speeds that might only be ~3-4% difference which is not a big deal.