Rob, thanks for getting those posted. I hope a few folks will take the time to fill out the Blood Trail Data Sheet and submit them. It's going to take a substantial amount of blood trail data to ever be able to come up with statistically meaningful results.
Chop, I’ll try to answer your questions point by point.
1. I’ve not noticed any problem with the longer inserts, when drawn onto the shelf, and a couple of my Ultra-EFOC shafts are at the very minimum length I can possibly use (simply because that’s the length the happened to tune at). I have encountered ‘false stiff spine’ with shafts that had a weak dynamic spine and were excessively long. In those instances the rear of the shaft was hitting the riser and causing the arrow’s flight to show a ‘too stiff’ point of impact. Shortening the shaft cures that, with the point of impact dropping from the ‘false stiff spine’ to showing a ‘weak spine impact’ and then, as the shaft is shortened more, a progressively stiffer dynamic spine until the shaft either tunes correctly or I run out of shaft length to shorten.
2. In the next Study Update there will be a detailed examination of what the data SUGGEST about the amount of penetration gain per percent increase in FOC; as FOC progressively increases.
3. I first bare shaft tune the shaft with a field point of matching weight and assemblage (same weight field point as the broadhead I am planning to use, same type and weight BH taper, if one is used, same insert, same internal footing, if one is used).
In my bare shaft tuning what I’m looking for in the un-fletched shaft is: (a) visually perfect flight (no wiggles, wobbles, flips, flops or flaps); (b) Fast recovery from paradox. I want the bare shaft showing straight impact into a uniform medium target by AT LEAST the time it reaches a distance of 3 yards – and often they will show straight line impact at distances as close as 3 feet – and I want it to maintain that straight impact at all distance back to 40 meters. This needs to be tested under calm wind conditions by shooting at each yardage back to 40 meters. (c) I want the point of impact at 40 meters to show only a very slight weak spine impact; no more than 2 to 3 inches right (for my right hand shooting; it should be left for a ‘lefty’).
Once I have a given EFOC or Ultra-EFOC arrow bare shaft tuned to my satisfaction I then fletch one of the field points up and verify that the fletched shaft shows matching flight against the bare shaft. On EFOC and Ultra-EFOC shaft I use 3 inch, parabolic cut four fletch on this test shaft. On normal/high FOC arrows I will use either 4 inch or 5 inch four fletch for this test shaft, depending on arrow FOC. This fletched, field point tipped shaft should now show perfect flight and impact ‘dead on’, left to right, at 40 meter.
Next I place a couple of the broadheads I will be using onto the shafts and fletch them up and check the flight against the bare shaft. I use the same ‘starting size’ fletching as I used on the fletched field points shaft. If all looks good with the broadhead’s flight I shift over to a ½” high, A&A pattern cut (without the turbulator) and begin to gradually reduce the size (total surface area) of the fletching until the first place I see a TINY AMOUNT OF INSTABILITY in the flight of the broadhead tipped arrow. At that point I add the turbulator, placing it 1/4" in front of the fletching. Almost always the turbulator immediately creates enough increase in air pressure on the fletching to again fully stabilize the broadhead's flight. If it doesn't, with the turbulator consistently maintained at ¼” forward of the fletching, I begin increasing the length of the fletching in 1/8" steps, maintaining the ½” fletching height, until I'm fully satisfied that the flight is stable.
When testing flight stability with the broadheads be sure to shoot a good number of shots, and I like to shoot the broadheads multiple times under various wind conditions (into the wind, with a trailing wind, cross wind and both into and with a quartering wind) until I'm totally satisfied that the fletching will stabilize the broadhead flight in all wind conditions, even when I get a less than clean finger release.
This sounds like a lot of work, but really isn't as bad as it sounds. After you do a few you get a pretty fair idea of what it takes for your individual shooting style and a particular broadhead. It goes fast after that, as you can often ‘shortcut’ the steps, based on previous experience. For example, I now know that, for arrows with an FOC above 25% FOC and a relatively ‘low wind sheer broadhead’, I can start out with 2.5”, four fletched, A&A cut-pattern feathers.
As well as the amount of FOC your arrow has, the amount of fletching (total surface area) you'll need is also dependent on the length of the arrow's rear steering arm. At any given amount of FOC, the longer your arrow’s shaft, or the closer your fletching is to the nock, the less fletching (total surface area) that is required. At any given amount of FOC, the shorter your arrow, or the further forward (in front of the nock) the fletching is placed, the more fletching required.
Here's a link to the TG thread on Fletching and EFOC. There's some information in there that may be of use.
http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=1;t=057257#000000 4. I have not tried the reflective tape but other folks that have say it works as well as the pinstripe tape. Best thing to do is top try it yourself and see how it works for you. I’m just a bit too lazy to cut the tiny, uniform width strips out. The pinstripe tape is just cut to length, peal and stick, securing the cut-end juncture with a thin smear of glue. Most hobby supply stores have the pinstripe tape.
5. As far as penetrating heavy bone, from the Study data the true critical point of broadhead Mechanical Advantage (MA) appears be 2.6, not 3.0. In the 2007 Update, Part 4, you can find a more complete discussion, in the sections titled The Importance of High Broadhead MA and Another Look at Broadhead MA’s Effect. Here’s the link.
http://www.tradgang.com/ashby/2007update4.pdf But there is one important thing to note; don’t confuse a 3.0 MA broadhead with what some folks term a “3 to 1 ratio” broadhead. With a single-blade broadhead, a “3 to 1 ratio” broadhead – that is, one that has a TOTAL cut width of 1” wide and a cutting-edge length of 3” - WILL have a MA of 3.0; but that’s not how some folks interpret “3 to 1 ratio” when it comes to multi-blade broadheads. Some folks seem to interpret “3 to 1 ratio” to mean that the height of each cutting blade is 1/3 the length of that blade’s cutting edge. For example, some folks will term a three-blade broadhead where each blade had a cut height of ½” with a cutting edge length of 1.5” a “3 to 1 ratio” broadhead; meaning that the cutting edge of that individual blade is three times the height of that individual blade. This gives THAT INDIVIDUAL BLADE a MA of 3.0, but it DOES NOT give the broadhead a MA of 3.0. The overall MA of such a broadhead is only 1.0! That’s because the total cut width of 1.5” equals the 1.5” length of the broadhead’s cutting edge.
It’s important to note that the data shows that ALL structurally intact, ‘above the heavy bone threshold’ arrows having broadheads with an MA above 2.6 penetrated the entrance side ribs in the buffalo testing; regardless of whether the broadhead was of single-bevel or double bevel design. The big difference between single-bevel and double bevel broadheads comes in the average amount of penetration achieved AFTER THE BONE WAS PENETRATED. Every 2.6 MA (and above) single-bevel broadheads showed greater average post-breaching penetration the ANY comparable double-bevel broadhead. Bevel type and design are major factors in breaching heavy bone; using less of the arrow’s ‘useful energy’ during bone breaching and retaining more of the arrow’s force for post-breaching penetration of the underlying tissues. A clear example is shown in the 2007 Update, Part 4, in the section titled Another Look at Single-Bevel vs. Double-Bevel Broadheads. There, the penetration outcomes of arrow setups that were identical, excepting only the broadhead’s type of edge bevel, are compared. Here’s that link:
http://www.tradgang.com/ashby/2007update4.pdf More specific to your question, in ‘all soft tissue hits’ testing the very narrow, very high MA (11/16” wide) Grizzly Extreme out-penetrates both the somewhat lower MA, 1” wide, Modified Grizzly and the still lower MA, production-profile, 190 Grain Grizzly. When tested on heavy bone hits that MA relationship does not produce the same outcome. There the Modified Grizzly out-penetrated both the narrower Grizzly Extreme and the wider-cut 190 grain Grizzly.
Heavy bone penetration becomes a balancing act, especially for the single-bevel broadheads. For penetrating heavy bone with single-bevel broadheads there is definitely a broadhead width factor involved. The wider a broadhead is (at a given length) the lower the broadhead’s MA, and the more arrow force required to penetrate the bone, but with the single-bevel broadheads there are off-setting factors. With single-bevel broadheads, the broadhead’s width affects the length of ‘lever arm’ for the lateral torque created by pressure differential of the bone (or other tissues) on the edge-bevel’s surface. Due to the differing angle of attack, broadhead width also affects the amount of surface area the edge-bevel will have in contact with the bone at any given instant during penetration.
The angle of the edge-bevel that you have applied to the broadhead also affects the amount of edge-bevel surface area in contact with the bone at any given instant during penetration. Thickness and density of the bone are also factors, working inversely to what many would assume. The thicker the bone the more of the bevel’s surface area in contact with the bone at any given instant, which means a greater pressure differential on opposing sides of the single-bevel blade, resulting in greater lateral (rotational) torque. The denser the bone the greater the pressure exerted between the bone and the surface area of the single-bevel’s edge; resulting in a greater rotational pressure differential and greater rotational torque.
These conflicting forces; resistance due to broadhead MA and bone density and thickness vs. the broadhead’s ability to generate sufficient rotational torque to split that given bone; are a delicate balance. I know of no way other than relying on outcome driven results from a huge number of shot into real tissues to determine what broadhead design gives the best results on the greatest number of outcomes. You can read more about this topic at
http://www.tradgang.com/ashby/2004update1.pdf and
http://www.tradgang.com/ashby/single-bevel-broadheads.pdf Hope that helps,
Ed
Topic: Barely Above Heavy Bone Threshold Ultra-EFOC Arrow (Read 11293 times)
