Will a 65lb bow be more efficient than a 60lb vs 50lb bow shooting an arrow??

[McDave]

One would think that grains per pound would be a good predictor of arrow velocity, but I have found this not to be true when comparing bows of different draw weights.  I like to tune my bows and arrows using arrows of about 9 gpp.  It seems the higher I go in bow weight, the lower velocity a 9 gpp arrow produces.  That is, typically a 40# target bow might produce 190 fps using a 9 gpp arrow, whereas a 50# hunting bow might produce 180 fps with a 9 gpp arrow (both of the bows recurves of comparable quality).  Is this just another reflection of the subject being discussed in these posts, that increases in bow weight produces diminishing returns in efficiency?

[pdk25]

Yes, but I think yours is an extreme example, and not likely to be seen across the board using bows of the same design. That would be amazing to reach that level of diminished returns at such a low draw weight.

[McDave]

Actually, the example I gave, while not based on any kind of a scientific study, is representative of more than a few bows in the 40# - 50# range.  Since I typically shoot targets with bows in the 40# range, and typically hunt with bows in the 50# range, and chrony all of my bows, I have come to expect that speeds obtained with 9 gpp arrows are going to be less with heavier bows than with lighter bows.  Maybe the figure I tossed out of a 10 fps difference is not correct, as I haven't done an actual mathematical analysis, but the concept is accurate, as it relates to the bows I have chronied.  Perhaps the reason is less because of diminishing efficiency as bow weight increases and more because of the physics involved in the force required to get a certain mass to a certain velocity (or perhaps a combination of the two)?

[Alexander Traditional]

I'm not real sure if this is what you guys are talking about or not,but I think it is. Pretty neat little video anyway.

 

[pdk25]

Dave, I am saying that for the same exact style bow with nothing altered, including string type and silencers, other than the poundage of the limbs, I have never seen a drop like you are  describing, even at highter draw weights.

[McDave]

Alexander, the YouTube video you linked to is on point.  Shooting various bow weights at 10 gpp, the arrow velocities recorded were essentially the same.  The arrow velocity was actually a little higher on the heavier bow, although the difference was probably statistically insignificant.  Obviously, my measurements were different, and I'll have to ponder why that might be.

In my own experience, I find that very heavy bows have a lower per pound/spine requirement.   While a lighter bow of the same design can shoot a higher per pound/spine ratio.  There is always some gain as weights go up, but as Byron Fergusson  stated, there is a point of diminishing returns.  I think that point varies with different designs.

[forestdweller]

Even if the heavier bow is 10fps slower it will still shoot flatter at longer distances because as an example, a 650 grain arrows sheds speed at a much slower rate than a 350 grain arrow would.

I'm of the opinion that arrow speed within 25 yards is mostly irrelevant though.

I personally can shoot both a 600 grain arrow and 450 grain arrow and there's practically no change in my POI within 25 yards and even at 30 yards the difference is negligible.

For me personally, around 35 to 40 yards is when arrow drop starts to factor in and I can tell the difference between different weight arrows.

But by that point I'd prefer the heavier arrow even if it's 10fps or so slower because it will be more stable in flight (wont be effected by wind nearly as much) and will shed very little velocity down range.

[YosemiteSam]

Originally posted by forestdweller:

I personally can shoot both a 600 grain arrow and 450 grain arrow and there's practically no change in my POI within 25 yards and even at 30 yards the difference is negligible.
 

My experience has been different.  My gaps are about twice as big going from a 655 grain arrow to a 550 grain arrow.  But maybe that's because my lighter arrows are shorter (amplifies the gap).

[Stumpkiller]

The way I see it . . .

If you have three bows: 65#, 55# and 45#.  Say you  kill a deer with each.  Then 45# is the most efficient of the three.   ;-)

[Longtoke]

McDave, have you tried comparing speed on your heavier bows with a heavier arrow as well? Just curious if they were slower than the 9 gpp arrow, like I would expect.

[McDave]

Originally posted by Longtoke:
McDave, have you tried comparing speed on your heavier bows with a heavier arrow as well?

Of course, when I compare arrow velocity at 9 gpp, I am shooting a heavier arrow out of the heavier bow.  But I get your point.  If I compared arrow velocity at 10 gpp or 12 gpp, it is possible that I might get a different result.

[John Havard]

Dynamic efficiency is strictly a function of the efficiency of your bow at a known grains-per-pound of draw weight at a specific draw length.  Dynamic efficiency isn't a standard number.  Different bow designs have different efficiencies.  But if you have a brand "X" bow at 65# and the same brand "X" bow at 45# it will shoot the same GRAINS PER POUND ARROW at the same speed if all other things are equal.  Same bow length, same string length and weight, same brace height, etc.

[McDave]

After watching the video that was posted, and hearing from others, I think my conclusions from my own testing were flawed.  I don't have two models of the same bow to test with, so I'm really mixing apples and oranges when I test a 50# brand A bow against a 40# brand B bow using 9 gpp arrows in both cases.  While all my bows are high quality, I may have a personal bias in selecting higher performance bows for my lower poundage target bows, and higher reliability bows for my higher poundage hunting bows.

But learning new things is a primary reason I participate in TradGang, and I think I just learned another one.

[sightsee]

Great discussion going on here!
One point I'd like to add.
Draw length plays a significant part on how an arrow performs.
A person shooting a 50lb bow at 28" draw compared to a person shooting a 50lb bow at 29.5" draw will for all practical purposes of this discussion will perform differently.

What do the experts think?

[Terry Green]

Just remember....a,diminishing return is STILL a return.

Yes, even though, at least for me, the spine per pound was less with the bows that were over 80 pounds, the increased arrow weight has a major effect on the penetration, or in my case the yards of pass through.  The last deer I shot with my 96 pound bow, up hill to a field edge with a dowel stuffed into the front half of a Microflite 12.  That arrow skipped and bounced a long way after going through the deer. Of course, a deer is in no way a 400 pound boar. I had that set up for moose hunting, then when I had the chance to take a very  easy shot, I couldn't do it.  Turns out I have a soft spot for moose.