How does Dr Ashby achieve 30% EFOC and still have enough spine?

[Matabele]

Just been playing with some Axis 400’s and achieved 28% FOC with 385gr up front. Shaft wasnt stiff enough however (55# @ 27” pulling 28” FireFly), and on the recommendation of wingnut I’ve been plugging some numbers into this calculator:

 http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=1;t=071556;p=1

The numbers say I should be going to a 340 spine shaft. Ok no problem I can do that, and still have a FOC of about 27%. But now Im wondering how does Dr Ashby achieve EFOC of 25-30% with the really heavy longbows he uses? Im not saying he’s not getting it, just wondering how.

Plugging the numbers into the calculator, even with a .300 shaft or the newer Axis Dangerous Game shaft, that spines at .250 (17.2gr per inch) which is about the stiffest on the market I think, these shafts appear not to be stiff enough. And the FOC with the DG shaft drops to a “measly” 20%, due to the high gr’s per inch.

Im curious as my next bow I order will be at 70#, and will be either a ACS or Swan which generally require stiffer arrows anyway.

Any thoughts appreciated.

[trapperDave]

the calculator is a guide, only actually bareshafting them will tell ya whats really up

[Jeremy]

You can always build out your sideplate to lower your spine requirement.

[Thueb]

I’ve read all the Ashby reports and if my memory serves, I thought Dr. Ashby defined EFOC as anything higher than 19%.  That was study defined as the FOC where there is a marked increase in the penetration of heavy bone.  Not that I have anything against 25-30%, but that seems "extreme extreme" FOC to me.  

I believe Dr. Ashby is getting 25-30% by using footed hardwood shafts, or by double shafting carbon arrows (using various sizes of aluminum shafts inside the carbon shaft), that would add to the spine of any carbon shaft.  Also tapered carbon shafts help with the FOC, but they are expensive.

This next statement is just an observation, and I don’t mean anything by it, but it seems to me that just like anything (arrow wt, FOC, bow wt, etc.) when you go to one extreme, or the other, you sacrifice something.  I believe in EFOC and shoot grizzlystick arrows with 200 gr points (right at 21% FOC, 680 gr total arrow wt), out of my 64 lb Bob Lee.  I’m not worried about FOC it as long as I’m above 17-19%.  With my current set-up I don’t worry too much about penetration.  Granted, I’m not shooting Cape buff with it, but I’ve been to Africa and wouldn’t hesitate to shoot an eland with it.

[James Wrenn]

You got to shoot short arrows to get those numbers with a bow that is not cut to center.Like you most would run out of spine otherwise.I only draw 27" and shoot lighter weight bows and I doubt if I could do it because my bows are cut past center.

[Matabele]

Thanks for the info guys. I was curious as I think most of Dr Ashbys testing was done in the 19-25% FOC range, but I distinctly remember a few references to 30%, and was curious as to how that might be achieved and still have enough spine.

I too think that once you're in EFOC territory (i.e. above 19%) you're good to go, much like getting weigh over 650gr which is the threshold for breaching heavy bone. Perhaps the gains are not as significant as to outweigh the disadvantages...in this case finding an arrow stiff enough.

[Daddy Bear]

I'm in the 27% range using AD Trad Heavies out of a 65#@27" Hill longbow drawn 27 1/2 inches. The arrows weigh 715grains cut about 28 1/2 inches BOP. I have room to shorten the arrows more so they'd probably work for a bit heavier bow and still get fairly high EFOC.

[sou-pawbowhunter]

Some of the prior responses touched on a very likely scenario.  The Good Dr., as some have observed, is using a very heavy longbow in his tests.  His bow is a rather straight limbed longbow,  probably not cut to center, much less past center as are many of our newer bows. Thus it will not require an arrow of such great spine.  Jeremy also pointed out in an earlier post that one could build out their side plate, on a bow that is cut past center this, would allow for the use of a lesser spined arrow.  I have been led to understand that Fred Bear would often tune his bow to the arrow in this fashion.  Hope this helps.

[Benny Nganabbarru]

The shelf needs to be built-out...

OR

You need really short arrows...

OR

Lighter poundage bow...

OR

Shoot Grizzlystik Safaris...