Post by BT on Jan 18, 2009 19:37:27 GMT -5
It's Ashby month again 
Below are the seven commandments as they relate to the compound bow according to Ashby .
Following each commandment are BT's assertions.
1) Maximize your bow’s efficiency: 12 to 14 grains of arrow mass per pound of draw weight is peak efficiency for most compound bows.
Building any system based solely on arrow weight will fail some while satisfying some.
On each end of the scale there will be excesses when using such a formula.
While a 40# bow will be shooting a 560grn arrow at the upper end of the stated range, a 80# bow will be shooting 1120grn. arrow.
Both bows would be shooting at a drop point of 20 to -20 yards and would have a shot window of 18+" with a 10yrd. pin gap
This rule also neglects to address the type of bow and how it relates to stored energy production.
Some compounds under perform top shelf recurves
2) Use broadheads of high mechanical advantage.
Again, any extreme is an extreme and by definition, extremes are not absolutes
Just as a 1/1 ratio head can act to stall penetration, so to can a 3/1 in a similar situation.
If 3/1 was the best based solely on ratio, why then are there not 5/1 ratio heads out there?.
There certainly wasn't an issue making the tree shark and other heads that exceeded 3/1....so where are they?.
The fact is that while 3/1 may be superior for flesh and soft bone....it adds excessive drag through dense bone.
3) Use broadheads with a cut on impact tip
Again, a generalization.
While the COC head is superior for soft penetration, the highest losses in Africa (before the creation of the Muzzy ) belong to the COC.
The trocar tip showed a marked decreases in wounds since their inception and usage in Africa, during that same time period.
The COC can be made superior and has been since but the statement COC (made by Ashby)does not carry conditions as to construction and design
4) Accept nothing less than perfect arrow flight. A tuned bow with proper arrow spine will ensure that minimal energy is lost due to flexing in flight.
Agreed
5) Do not use mechanical broadheads. In testing, mechanicals were the most prone to breaking, which stops penetration cold. They have a poor mechanical advantage as well, and require additional energy to deploy.
You have to remember Ashby's rule or you might think that he meant every and any fixed head is superior...which couldn't be further from the truth
In percentage terms, the expandable has out performed the fixed replacement blade market in terms of structural integrity.
Thats a plain and demonstrated fact that can easily be found in past testing.
That said, the expandable is weak but not the weakest of the four designs.
The above statement is (once again) a coverall that just does not hold water
While fixed blade heads such as the Grizzly may well be the strongest designs out there, the vast majority of fixed blade heads are weak and do not carry the best design characteristics as relates to ratio.
As for the expandable line up, the vast majority carry 2.0+ ratios and are superior as to impact resistance in view of damage to the head on the entry side of any dense bone.
6) Use an arrow shaft smaller in diameter than the ferrule of the broadhead.
Agreed
7) Shaft finish – basically, the smoother, the better – there is less resistance.
Agreed
Below are the seven commandments as they relate to the compound bow according to Ashby .
Following each commandment are BT's assertions.
1) Maximize your bow’s efficiency: 12 to 14 grains of arrow mass per pound of draw weight is peak efficiency for most compound bows.
Building any system based solely on arrow weight will fail some while satisfying some.
On each end of the scale there will be excesses when using such a formula.
While a 40# bow will be shooting a 560grn arrow at the upper end of the stated range, a 80# bow will be shooting 1120grn. arrow.
Both bows would be shooting at a drop point of 20 to -20 yards and would have a shot window of 18+" with a 10yrd. pin gap
This rule also neglects to address the type of bow and how it relates to stored energy production.
Some compounds under perform top shelf recurves
2) Use broadheads of high mechanical advantage.
Again, any extreme is an extreme and by definition, extremes are not absolutes
Just as a 1/1 ratio head can act to stall penetration, so to can a 3/1 in a similar situation.
If 3/1 was the best based solely on ratio, why then are there not 5/1 ratio heads out there?.
There certainly wasn't an issue making the tree shark and other heads that exceeded 3/1....so where are they?.
The fact is that while 3/1 may be superior for flesh and soft bone....it adds excessive drag through dense bone.
3) Use broadheads with a cut on impact tip
Again, a generalization.
While the COC head is superior for soft penetration, the highest losses in Africa (before the creation of the Muzzy ) belong to the COC.
The trocar tip showed a marked decreases in wounds since their inception and usage in Africa, during that same time period.
The COC can be made superior and has been since but the statement COC (made by Ashby)does not carry conditions as to construction and design
4) Accept nothing less than perfect arrow flight. A tuned bow with proper arrow spine will ensure that minimal energy is lost due to flexing in flight.
Agreed
5) Do not use mechanical broadheads. In testing, mechanicals were the most prone to breaking, which stops penetration cold. They have a poor mechanical advantage as well, and require additional energy to deploy.
You have to remember Ashby's rule or you might think that he meant every and any fixed head is superior...which couldn't be further from the truth
In percentage terms, the expandable has out performed the fixed replacement blade market in terms of structural integrity.
Thats a plain and demonstrated fact that can easily be found in past testing.
That said, the expandable is weak but not the weakest of the four designs.
The above statement is (once again) a coverall that just does not hold water
While fixed blade heads such as the Grizzly may well be the strongest designs out there, the vast majority of fixed blade heads are weak and do not carry the best design characteristics as relates to ratio.
As for the expandable line up, the vast majority carry 2.0+ ratios and are superior as to impact resistance in view of damage to the head on the entry side of any dense bone.
6) Use an arrow shaft smaller in diameter than the ferrule of the broadhead.
Agreed
7) Shaft finish – basically, the smoother, the better – there is less resistance.
Agreed
