Anyone else see a trend here ( different arrows momentum)

[Toehead]

#3812

First let me say that these arrows are not “tuned” to the bows they were shot, FOC isn’t being considered either, this is a straight Momentum comparison. The two bows are the same model, made by the same bowyer. The first is marked 58@26.5″ drawn to 28.25″ using a clicker. The second is marks 51@28 drawn to 29″ using a clicker. However in my opinion bow weight is irrelevant for the data.

I shot each arrow 5x through the chronograph from the same distance (~3′), trying to hit the same point on the bag for consistency. The high and low shots were thrown out. The remaining 3 shots were averaged for the fps variable. All arrows were weighed on a calibrated weight scale and the momentum calculations were done using the Vintage Archery Calculator on the website.

Bow 1

Arrow 1: 459 grains, momentum .38 ft-lbs/s

Arrow 2: 541 grains, momentum .42 ft-lbs/s

Arrow 3: 647 grains, momentum .48 ft-lbs/s

Arrow 4: 759 grains, momentum .52 ft-lbs/s

Bow 2

Arrow 1: 353 grains, momentum .32 ft-lbs/s

Arrow 2: 464 grains, momentum .38 ft-lbs/s

Arrow 3: 558 grains, momentum .42 ft-lbs/s

Arrow 4: 650 grains, momentum .46 ft-lbs/s

Arrow 5: 750 grains, momentum .50 ft-lbs/s

Ok a couple of questions.

After the first bow run I got excited to see he momentum jump from arrow 2-3. So I tried it with the second bow and the trend pretty much stayed steady.

So what is it about 650 grains that makes it the breaking point so to speak? Maybe I should study the study more.

How much difference does .02 ft-lbs above 650 grains?

If I kept plotting this out with heavier and heavier arrows would I be able to show the point of diminishing returns?

I apologize if this is all on the lethality study and I need to read it again.

It is nice to have a place where the unbiased can weigh in.

Gracias.

[Ed Ashby]

#24045

The Heavy Bone Threshold is not a precise function of either the KE or Momentum. Most arrows carry enough KE and Momentum to breach a heavy bone, if that force and energy is applied to the bone long enough. The Heavy Bone Threshold is a function of how long the arrow maintains its ‘forward push’. It’s the Time of Impulse that matters, i.e. how long the arrow is able to continue ‘pushing’ on the heavy bone, after impact. That’s a function of the arrow’s weight.

The heavier the arrow the slower it loses its velocity and the longer it can ‘push’ against the bone. The arrow has to ‘push’ on the bone for a long enough period of time to overcome both the movement of the bone at the attachment and the flex of the bone. Only after as bone has reached its limit of movement can the arrow begin to breach the bone.

The data indicates that, to consistently breach a heavy bone (with any broadhead having a MA of 2.6 or more), the amount of arrow weight required to attain the necessary Time of Impulse is at, or very, very close to 650 grains.

Ed

[Toehead]

#24097

That makes sense! Thank you.

[Col Mike]

#24325

I hesitate to add to Dr. Ed’s informed response–but from my experience without the aid of a any devices the heavier the arrow with most weight up front means max penetration. So with 500gr up front total arrow 775gr–carbon of course–they shoot were I point them. And punch thru whatever target I give them.

So forgive an ole tankers reminding: our primary armor defeating round the APFSD, is so many inches long with a heavy Depleted uranium point–as my memory remembers about 60% Efoc–of course it’s flying at 1500 m/sec but that puppy penetrates a Russian T-72 at 3000m.

Having read all of Ed’s reports–I can only say that heavy with most of that weight forward ensures an ethical kill.

Have fun with that–Joe Furlong offers all those weights in field points with multiple adapter weights which make the experimenting fun and informative.

Semper Fi

Mike

[Author]

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