As for the most common shaft diameters for crossbow arrows, I thought the 11/32 shaft was more common than the 3/8's that you were specifying (.343 versus .375), but I'm going by insert sizing not actual shaft diameters. My guess is that you are using the actual shaft sizing, is that correct?
Like you, in my humble opinion and that of some long time industry experts, it would stand to reason that a heavier shaft propelled at a slightly slower rate of velocity would provide better spine deflection and a more stable flight. This would also yield much better penetration capabilities due to the shaft carrying a greater amount of Kinetic Energy over the distances.
We were almost ready to test these crossbows using one of Easton's top of the line Hunting Shafts. They were one of the N-Fused Carbon Core shafts (Axis Full Metal Jacket - Dangerous Game Shafts). They are Easton's heaviest shaft with a .002 straightness factor from beginning to end. They are available in two shaft spine sizes (.250 and .300) and are factory sorted by spine and weight, and properly marked and indexed. The only gotcha was the shaft diameter is only 9/32's which won't support the needed 11/32 nocks to operate the PSE TAC15 Anti-Dryfire mechanism on the TAC15 cranking block.
The thought was to see how these shafts would both group at medium and long distances and their overall performance in comparison to the very light TAC shafts being used by PSE.
I'm still working on a shaft alternative, but as you now understand alternatives don't grow on trees for this beast.
I think one think you might consider when shooting alternative shafts is not so much the weight of the shaft (unless it is less than the 422 grains over all) but the spine. There is no way a .250 spine is going to survive the G-forces of the launch in my opinion. As we already know, the power to weight ration is way off the standard. It might make it out of the bow, but which direction it will be pointed is anybody's guess due to the extreme flexing that will take place.
That is just my opinion and not fact so you won't know till you try it. And the problem with the TAC nock is not that it is 11/32, it is the size of the throat that makes it unique. A standard nock would work to deactivate the anti-dryfire, but it will not lock onto the string due to the serving size being so large. If you got rid of the extra wrappings they put under the D-loop, you might could use a larger variety of standard nocks.
You are totally correct on your spine assumption for the .250 shaft.
I was hoping the .300 might work, but the shaft diameter also plays a big roll in the stiffness factor. That's what I was stating in my last response to Konrad when we were talking about the 11/32 (.375) shaft sizing being used for most crossbows. Most manufactures seem to be using the wider shafts to achieve the stiffness needed to handle the extreme torque produced by today's crossbows.
When you do the math on these things it adds up to some very extreme numbers, so if I'm reading the numbers correctly, it also puts some limitations on what we can or can't play with from an alternative shaft perspective.
I'll wait to hear what Konrad has to offer based on his research, but I'm fairly certain he's going to tell us that our best bet is still to sort these arrows by matching the spines and re-fletching them accordingly after indexing the nocks to the spines.
If not, I'm always willing to learn something new and we're definitely on the right website for that.
I learned something new today:
Easton is now offering FMJ shafts of a larger diameter for crossbows. The factory shaft diameter for the Easton Full Metal Jacket Bolt is 11/32 diameter.
When I first made the suggestion about using the Easton FMJDG, I was unaware the smaller diameter would present mechanical issues. These new crossbow shafts are offered in either 20 or 22 inch lengths.
My 2010 Easton catalog does not list this shaft.
The web site lists the bolts as 13.7 gpi and that falls between the 300 and 250 when going by gpi weights alone. I am willing to bet this is a response to the TAC shooter’s demands. As to the nock issue, I’ll also bet some combination of nock/bushing could be sized properly or an Easton product is forthcoming. Without knowing the shaft ID it is difficult to know what nock combination would work. Perhaps the anti-dry fire mechanism could be temporarily by-passed for shaft evaluation purposes.
You were right in correcting my comments about shaft sizing. 24/64 is actually .375.
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Once again, surprising information. I have a couple of quick points on the new Easton FMJDG's. As long as the new shafts are 11/32's we have no issues because we could use Firenocks or the standard PSE Nocks, but I would lean toward the Firenocks for a number of reasons. The work fine and present no problems with the anti-dryfire mechanism.
A quick item to help everybody cheat a little when doing decimal to fraction conversions or the reverse: If you go to your "Google Browser" and go to the search bar and type in any decimal or fraction and just hit enter, it will instantly do the conversion for you, so it doesn't take any math skills to figure out these sizings.
Sorry for the deviation Konrad, I was trying to help some of the non engineering types that may follow this thread. The new shafts that Easton will be producing only has one possible flaw that may be a problem. We need them in the 26.25 length, so do you know if they will produce them as full length shafts that can be cut to length or will they only be available in the lengths you specified? If you don't know, don't go crazy chasing an answer, I'll know the answer probably by tomorrow late afternoon. I have some TAC shaft testing scheduled with somebody who might know something about these new shafts.
I think the .300 is a spine deflection measurement, but no necessarily a fixed diameter measurement. I thought a manufacture could potentially obtain a given spine rating on arrows of different diameters, such as the current Easton FMJDG's which can be ordered in either .250 or .300 spine, but until this new news they were all 9/32 diameter shafts. The weight per inch was much different between the 2 shafts sizes, due to the thickness of the shaft walls, which is where the extra stiffness in the spine comes from.
The way the N-Fused Carbon Core is created is different than the PSE Woven Filament Shafts, but it's similar in the respect that it's designed to be extremely strong and durable. Another key difference is the straightness factor of the Easton Shaft at .002 measured end to end, which no other manufacture uses as stringent a measuring system. Also keep in mind that these shafts are a metal outside with a carbon core. This is where the extra weight comes from that makes them usable for the largest big game animals.
As we know, when it comes to the very best of the best in competition arrows .001 is as perfect as has ever been produced, so we are bordering super high grade competition arrows with these new offerings.
Although I'll finish testing and analyzing the PSE TAC arrows until we know everything about them, I will switch in a heartbeat to the arrows we're talking about if I find they become available in the 11/32 size in a full length version.
There's a high probability Easton may be looking for some outside field testers.