Momentum question?

[JamesKerr]

What was the momentum value that Dr. Ashby found was the bone breaking threshold. For some reason I remember it as being .4 .

[BOHO]

bump for you cause I have no clue. hope you can find your answer. did you try and google it?

[awbowman]

I was thinking it was over .5, almost .6.  I'm going to try and find it in one of his reports.

[JamesKerr]

Awbowman I have used the formula and to get a 650 grain arrow to produce a value of .5 it would have to be going close to 175 fps. I don't know of many bows in even the 60 pound range that will shoot a 650 grain arrow that fast.

[old_goat2]

Originally posted by JamesKerr:
Awbowman I have used the formula and to get a 650 grain arrow to produce a value of .5 it would have to be going close to 175 fps. I don't know of many bows in even the 60 pound range that will shoot a 650 grain arrow that fast.

If u have a long draw it will, mine shoots 182fps and I pull around 60lbs at 30.5" with a 615 gr arrow. Shot a heavier arrow same speed with spider legs, have beaver silencere now and wool wraps on end of string.

[vintage archer]

THE 650 GRAIN ARROW WEIGHT WHICH  IS THE THRESHHOLD FOR BONE  PENETRATION IS A STAND ALONE FIGURE.  INCREASING ARROW SPEED  DID NOT SEEM TO CHANGE THE NEED FOR AT LEAST  650 GRAINS  TOTAL ARROW WEIGHT.

[JimB]

That is what I was thinking.I didn't remember any specific momentum value.

[awbowman]

Maybe what I am thinking of was his earlier studies on buffalo.  I got busy and had to quit looking.

I don't remember his 2012 talk listing any momentum values, just a 650 grain arrow.

[JamesKerr]

Thanks Joe. I just thought I had seen somewhere before that there was a momentum value associated with the bone breaking threshold. My thinking was that if a 600 grain arrow shot fast enough to produce the same momentum as a heavier arrow shot slower, than they should both penetrate equally.

[COOCH]

Nope Joe is correct 650 grains plus is the number you are looking for.

[CoilSpring]

[awbowman]

1996 Ashby Report makes this statement concerning "adequate" performing broadheads


TO ACHIEVE .57 POUND-SECONDS OF MOMENTUM:  (The average momentum of the "Adequate" performing arrow/broadhead combinations in Natal Study, all of which had broadheads of 3.0 mechanical advantage and shafts equal to, or smaller than, the broadhead ferrule in daimeter)

In the initial reports he is not talking about "bone breaking" momentum, but more about penetration and lethality of hits.  He now appears to concentrate on a 650 grain arrow minimum.

[vintage archer]

It is not easy to wrap ones brain around some of these concepts. I questioned Dr. Ed Ashby at Kalamazoo about the same thing.

In my mind this is one of his most important research findings. It applies no matter what your FOC is, what type of broadheads you use or how fast a bow one shoots.

Yes the details such as broadheads, speed and FOC, all contribute but are just refinements of the 650 grain threshold.They are realy the frosting on the cake.

Example would be a arrow with UEFOC (30% weight forward) at a total weight of 650 grains would be ideal for penetration as FOC helps increases penetration in soft tissue and helps the arrow in bone once it is breached. It still comes down  to the fact no matter how you get it the total arrow weight of 650 grain or heavier is the goal.

For wood arrow shooters this is an important concept. It is hard or almost impossible to attain the refinements such as High FOC with wood arrows but the 650 + weight is easily attainable.

For archers shooting lighter bows attaining arrow weights in 650+ will give reasonable momentum for penetration and bring you to the bone breeching area. Additional weight or speed of course increases momentum. For most of us working on the weight side of the momentum formula is going to be the most practical.
 
Sorry for being so windy I just wanted you to know that it is easy for all of us to get confused with all the information that is out there.              

[JimB]

"A substantial
increase in the momentum of a below-threshold arrow, achieved
through increased arrow velocity, shows little effect on the
Heavy Bone Threshold. Increasing arrow mass to above-threshold
value has a pronounced effect on the Heavy Bone Threshold, even
when total momentum is reduced"

James,you might be interested in reading this:
 http://www.tuffhead.com/ashby_pdfs/ashby%20ours/2008%20Update.%20Part%201.pdf

[JamesKerr]

Thanks guys, I am going to be building up some new arrows soon and it looks like they are going to come out very close to 650 grains.