Edge bevel and the all soft-tissue hit.

[Ed Ashby]

#5637

Someone asked me a question about offset edge bevels and soft-tissue penetration loss due to the energy a single-bevel uses up rotating through the tissue. I though this was a subject worth a thread of its own.

Besides the normal double-bevel broadhead edges I’ve tinkered around with such things as offset double-bevels (one side of the bevel wider than the other side) and back-side micro-bevels (which is a single-bevel having a back-side bevel that is, literally, too small to be seen with the naked eye). I prefer a true single-bevel. It shows far better overall average results in all testing than do the offset bevels. However, the micro-bevel seems to work just about as well as a true single-bevel, if not fully as well.

A good source of information regarding the bevel designs would be Sharpster (Ron Swartz at KME Sharpeners). By the way, the KME knife sharpener (not the BH sharpener) is the easiest way to get a “truly sharp” edge on the single bevel broadheads, and is the perfect tool for doing the micro-bevel edge.

A lot of folks seem to think that the rotation caused by a single-bevel decreases the amount of soft-tissue penetration, compared to an equal profile double-beveled BH. On the surface, their reasoning sounds plausible; part of the arrow’s energy is used up in the rotation, leaving less energy for arrow penetration. Testing doesn’t support that contention. Here’s what they overlook.

In living (and very, very fresh) muscle tissues are muscle fibers are very taut, even in their ‘relaxed state’. They retract when cut. The tighter the muscle fibers are tensioned the easier they cut, and the greater the degree of retraction at the instant they are severed (the same as with a rubber band). The degree of muscle fiber retraction affects both the degree of tissue pressure on the trailing shaft and the ease of shaft-lubricating blood flow in the wound channel.

All broadheads enhance the tensioning of the muscle fibers as they penetrate, increasing the effectiveness of their cut. This they do because of the wedge effect of the ferrule and the blade profile during penetration. This wedge effect spreads the tissue, increasing the tension of the muscle fibers against the blade’s edge, making the cutting easier. This is true for both single and double-bevel broadheads.

Single-bevel broadheads have an additional tissue tensioning effect that double-bevel broadheads do not have. The bevel-induced rotation of the blade further spreads and tensions the tissues, further increasing the degree of tissue-tension against the blade’s edge. This is why single-bevel broadheads so often exhibit a soft tissue cut width that drastically exceeds the blade’s maximum cut-width.

In addition to their tissue-tensioning advantage, single-bevel broadheads generally have a much lower overall edge angle (a thinner edge – which is why they need to be made of better steel than a double-bevel, to make their thinner edge durable). This lower edge angle edge means the edge bevel itself has a higher mechanical advantage. At ‘equal sharpness’ and equal tissue-tension the lower cut-angle edge severs the tissue more efficiently; ergo, it also requires less blade-to-tissue tension to cut with efficiency equaling an edge of lesser mechanical advantage.

As testing indicates, the net result is that the single-bevel broadheads show a slight, but consistent advantage in soft tissue penetration, over a like-profile double-bevel BH, but the soft tissue single-bevel penetration advantage is nowhere near as significant as that shown during bone hits. In testing all results were consistent. This included testing of single-beveled Deadheads vs. matching double-beveled Deadheads; the 189 Ribtec Pro Big Game (which is a precise profile match to the 190 Grizzly) double-beveled at 12.5 degrees (for a 25 degree total bevel angle) vs. the 190 Grizzly with a 25 degree single-bevel edge; and the single-bevel vs. double-bevel versions of the Outback Supreme and Outback Hunter broadheads. In all test the single-bevel broadheads bested the penetration shown by double-bevel versions, on both soft and hard tissue hits.

While it is on heavy bone hits that use of a single-bevel broadhead shows the greatest penetration advantage, it also exhibits an advantage on an all soft fresh-tissue hit.

Ed

[J-dog]

#43142

Thank you for what you do!

Jason

[Treetopflier]

#47673

Ed — Another great explanation of the “invisible” working of physics, thank you. So, in addition to offering a slight penetration advantage in soft tissues, I presume it’s also true that we also have the considerable advantage of a longer cut channel insofar as the broadhead is “screwing” its way through the tissues rather than punching straight through. And finally (?) you’ve spoken of the enlarged exit wound resulting from the head twisting-up the taught skin around it as it passes through. Thus, it’s hands-down single bevel no matter the density of tissue impacted. Thanks! Snuffs

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