Dr. Ashby's12 arrow penetration factors were strenuously researched, tested and ranked in order of importance. Regardless of the manufacturer or the products, if you follow Dr. Ashby's 12 rules - you will have more bowhunting success.
All 12 points are insights are ranked in order of importance. Each of the 12 points is discussed by Dr. Ashby himself and taken from his 30 years of empirical bowhunting research.
Ashby Rule #1 - Structural Integrity
The most important factor of arrow penetration is structural integrity. If any component of your arrow fails penetration either completely stops or is greatly reduced.
Ashby Rule #2 - Arrow Flight
If an arrow is not flying perfectly it’s wasting valuable energy that could have contributed to penetration. If an arrow impacts before it has achieved perfect flight, energy is wasted that could have contributed to forward momentum and penetration. Perfect flight is crucial, you must achieve it no matter what the cost. Pay close attention to the other factors too though or you may find yourself shooting arrows that fly perfectly but can’t penetrate well at all.
Ashby Rule #3 - Arrow FOC (Forward of Center)
Tests have shown that EFOC, defined as 19% - 30% forward of center and Ultra EFOC, defined as over 30% forward of center enhances penetration from 40% to 60+%.
Ashby Rule #4 - Broadhead Mechanical Advantage
Long narrow broadheads have an advantage over shorter wider heads. It takes less energy to push them through an animal. That is their mechanical advantage. This is second only to EFOC and Ultra EFOC as a penetration enhancing factor.
Ashby Rule #5 - Shaft Diameter to Ferrule Diameter Ratio
You’ll lose up to 30% of your penetration potential if the shaft is larger than the ferrule where they meet. It’s best to be slightly smaller in diameter than the ferrule of the broadhead.
Ashby Rule #6 - Arrow Mass or Weight
Heavier arrows absorb more energy from the bow at the shot & they carry their momentum better than lighter arrows so they penetrate better. Bowhunters should use the heaviest arrow that will deliver a trajectory they can live with.
Ashby Rule #7 - Broadhead Edge Finish
Broadhead edges that have been honed and stropped smooth have a 26% advantage over smooth filed edges and a 60% advantage over the coarse “serrated” Howard Hill edge.
Ashby Rule #8 - Shaft Profile
On all shots, tapered shafts show an 8% penetration gain over parallel shafts and a 15% gain over barrel tapered shafts.
Ashby Rule #9 - Broadhead/Arrow Silhouette
Smooth transitions and slick arrow finishes greatly enhance the penetration potential of your broadhead/arrow combination. Broadhead ferrules with bumps or any irregular surfaces impede penetration, especially in bone.
Ashby Rule #10 - Type of Edge Bevel
Only if no bone is encountered does this factor rank 10th. If bone is hit, and more often than not it is, this factor jumps up toward the top of the list. If you can’t get through the bone, penetration stops. The powerful rotational force of single bevel broadheads splits bone. Single bevel broadheads regularly turn what would be a wound into a killing shot. Note: Your arrow must be of sufficient weight and strength to drive the broadhead through and withstand the forces involved in breaching the bone.
Ashby Rule #11 - Tip Design
In all testing where a bone was encountered the Tanto tip performed best. It resisted damage and skipped less than any other tip design.
Ashby Rule #12 - Heavy Bone Threshold
When soft tissue is hit, this factor is ranked last in importance BUT if a heavy bone is hit it will be near the top of the list. Heavy bone is almost impossible to breach unless you have 650 grains or better in mass arrow weight.