FOC and grains question:

[NorthernCaliforniaHunter]

Yeah, I'm the guy BTH has been talkin' smack (though nicely worded) about.    

A bit of advice needed:

Here's the deal, despite my bow saying 49# @ 28", it drew 45ish on a scale at about 29.5" (my draw length). I say ...ish because I don't trust the method behind our measurement, but it confirms a few things which I'll spare y'all the details of here.

Now, I'm shootin' carbon express 4560's, full length, weighted like heck at the nose. Using a familiar web based FOC calculator, my lighter built arrow roughly 566 grains (roughly because I have a gram scale, and I convert using 15.43 grains/gram), comes in at 20.4% FOC using field tips and an overall arrow length of 34".
Using broadheads, the same weight arrow, now measuring 35.75" reads an FOC of 14.6%

Increased weight on second arrow, all at the nose (now roughly 645 grains), and FOC's come in at 20.5% for field tip (shorter overall arrow) and 17.4% for broadhead (longer).

Here's the question      thanks for stikin' with me thusfar     ... Will I increase FOC by shortening the arrow (decrease of 9.9 grains per inch) perhaps down to an ideal length...

And, second question, is there an "ideal" length? Also, if at 20' range, increase in weight didn't seem to change trajectory or impact, should shortening by an inch or two also not necessarily change impact(due to a change in spine?)

Thanks guys, and Toby, do you know of an good therapist? Note the time of this post? I SHOULD BE ASLEEP!!!    

[just_a_hunter]

Ya lost bout the first time you typed a %.

But IF I think I understand you correctly, yes shorter arrows with the same grain at the tip will increase FOC.

But, as you mentioned, your spine will stiffen probably requiring more weight to be added up front.

If you are getting perfect arrow flight with your original set up, my advice would be to sharpen your broadheads and go hunt. You have enough for those Tx. hogs.

Good luck and have fun down there!

Todd

[James Wrenn]

Will I increase FOC by shortening the arrow (decrease of 9.9 grains per inch) perhaps down to an ideal length...
 

Yes. Shortening an arrow increases FOC with the same weight out front.Shortening it also stiffens it up so more weight is needed out front. That raises FOC even more.Much easier for a short draw guy to get heavy foc than someone that has to shoot long arrows.

[just_a_hunter]

I forgot to add that a shorter arrow with the same weight up front does indeed increase your GPI, but keep in mind you also loose a little weight when you chop your arrows. I don't think any animal will be able to tell the difference between an inch in your arrow length as long as you are getting perfect arrow flight.

I'm sorry if my advice is way off base of what you were trying to ask.

Todd

[R H Clark]

I know high FOC is desired but don't sacrifice a good tune to get it.You might negate any benefit that a little higher FOC would give.

It doesn't take much length to change the tune of a carbon shaft.I've shaved as little as 1/4 inch and seen a difference.If you shave two inches you may not even be able to add enough weight to tune again.

[NorthernCaliforniaHunter]

Sorry I lost you guys...

It was stupid-late to be up!

Here's the gist: If I understand correctly something happens (bone crunching) at around 600 grains and over 20% FOC, which is my goal.

Shorter would be better only because the arrows stick so darn far out of my quiver! (Monkey-man)

Thanks for the replies this far.   :D

[xtrema312]

With your bow only pulling 45# it kind of sounds like you are battling that 4560 arrow spine a little when you try to shorten those arrows.

[Buckeye Trad Hunter]

I didn't realize there was a BTH username on here.  I was about to apologize for something I didn't know I did  

[fatman]

I believe that the FOC calculator in Dr Ashby's report uses length of Nock Valley to Back of Point.  I think now I understand why...this eliminates the differences that you're getting by using overall arrow length....    

just an observation....

[NorthernCaliforniaHunter]

thanks fatman,
I was confused about that one, and still am. Since the b.h. or field point form part of the arrow, and I'd assume its aerodynamics, shouldn't it be included in the formula? The center of gravity on an aircraft is measured from nose to tail, not just fuselage... but I am certainly not the resident rocket scientist!

[SlowBowinMO]

Kevin is right, Ashby calculates FOC using the back of point.  There is some good discussion over whether or not that is the best way to do it, but if you are trying to match Ashby's FOC suggestions realize he's using BOP which eliminates the variation you're getting anyway.

Another great point above, don't sacrifice tuning in the interest of upping FOC.

[BTH]

Poor Jade    

Best therapist I know of is to sharpen your broadheads and go kill a Lake Sonoma hog!    

Go shoot something with that thing already!        

   

You get some pork, I'll go out to Hog Island and get some oysters, and we'll grab some Guiness and have a party.      

[NorthernCaliforniaHunter]

It won't be half as satisfying without a witness! Are you coming with me? SATURDAY!!!

(Besides, I was thinking so long as I can outrun you, I won't have to outrun a 300 pound boar with an arrow stuck out the side an inch short of the vitals.    )

[fatman]

Yeah, go kill somethin'....    

good luck!
 

[NorthernCaliforniaHunter]

Nice! Excellent feedback, gentlemen. I'm going to see what the calcs. work out to using back of point for the measurement. Considering I'm so close to 650grains and 20% FOC as it is, and since they fly pretty well, I'm going to put away the tinfoil hat and just work on making sure the points land where I'm looking!

  :rolleyes:

[NorthernCaliforniaHunter]

Now how do I correct form issues attributed to being cross-eyed, bow-legged, club-footed, and possessin' of all thumbs?

 

[BTH]

Sorry Brother, can't help you with all of that. Hey, don't be worried about runnin' faster than me...I'll just step aside since that hog will be focused on you!