The little things

[D-Rock425]

I added 40 grains up front on my hunting arrows last summer and noticed a huge difference in down range arrow grouping.  I was so concerned with getting speed out of my T-Rex arm draw  my foc was way under what it should have been.  I turned my bow up to 67# and added 40 grains up front that put my foc up to about 13.5%.  Speed isn't everything i thought it was.

[pd]

Tagged.

[D-Rock425]

So rav have you found a percentage where you loose advantage of foc..?

  i've always wondered about this myself.

[bullfisher]

I've been shooting over 19.5% FOC since 2009. Its hard to achieve and makes FOC the focus of the arrow build from the beginning, but the benefits of doing so are tremendous. The focus today seems to be on 100grn BH's, the lightest inserts and heavy illuminated nocks, resulting in the opposite. 

[earlmarne]

I just built me an arrow thats sitting at a little over 18.50 % foc. I am not a good enough shot to tell one way or the other but it sure makes getting my broad heads flying with my field points a ton easier.

[RadSav]

FOC – Front of Center (Part 2 of 2)

While storing energy in the right place is obviously beneficial it is only half of the FOC story.  Leverage is a large part of the FOC equation as well.

If we have an FOC of 10% that means we have 10% more energy stored in the front half of the arrow than we do in the back half with a mechanical leverage of 1.5X on the fletching end of the shaft (60/40=1.5).  It is in that leverage number we really see the difference between magic and troubled flight in varied environments.  The higher the leverage number the more difficult it is for opposing forces impacting the broadhead to affect the stability of the entire shaft.  In my personal opinion there is always a level of compromise wanted between the leverage number and speed/trajectory.  However, there really is no such thing as too high a number unless it adversely affects the arrows spine.

If our arrow were to be balanced dead center it would have an FOC of zero and a neutral mechanical leverage (50/50=1). So not only would the front half of the arrow have no energy advantage, but the back half would have no leverage advantage either.  This is desirable in anemometers and pinwheels but not so much in arrows meant for down range targets.
 
An arrow with an FOC of just 5% (55/45) would have 5% more energy in the front and the fletching would have an approximate 22% leverage advantage over the front.  FOC of 10% the fletching would have an approximate 50% leverage advantage over the front.  And at 15% FOC the fletching would have an approximate 80% advantage.  Knowing that, you can see how fast we can improve the leverage the fletching has with every 1% of FOC we add.

The magic really seems to happen at a mechanical leverage of 1.5.  However, since friction on the broadhead and friction on the fletching are constantly changing the balance of energy so does the virtual fulcrum point of leverage.  From my experience I believe this fulcrum variance usually falls between 2 & 5% depending on broadhead and fetching size (number of blades and fletching as well).  That being the reason I recommend a 12-15% FOC instead of just being happy with 10%.

[RadSav]

So rav have you found a percentage where you loose advantage of foc..?

If weight and speed remain constant your only loss should be in a weakened spine.  Possibly putting you weak for one arrow yet too stiff for the next arrow.  Gravity is not going to pull any faster just because you have more weight in the front rather than distributed among the length of the shaft.

If you can not simply take from the back and apply to the front there does tend to be a point where the loss of speed is greater than the benefit in return.  I've really not seen any advantage when I've gone above 15% in FOC in a center shot bow.  There does seem to be some advantage up to around 20% in the traditional bows I have shot.  But even then I'm usually fine tuning spine rather than making the most of a few percentage points above 15 FOC.  A good compromise is usually in order...even in traditional bows.

[RadSav]

Speed isn't everything i thought it was.

Obviously!  Seeing as how you have been shooting a Hoyt the whole time.

[D-Rock425]

Speed isn't everything i thought it was.

Obviously!  Seeing as how you have been shooting a Hoyt the whole time.

can't get anything past you!  As I typed that I said Rads going to rip me for this.

[RadSav]

All in fun!  I find myself shooting my Bear Truth2 and Dark Horse more often than not.  I think those are rated at 318 or something close.  I'll take accuracy over speed any day.  Although I do refused to pay $1,400.00 for a bow that is neither more accurate nor faster than the one I have just to improve my social standing among range commandos'

[RadSav]

I am surprised the new Hoyt Nitrum hasn't been talked up more this year.  Seems Prime and Elite are taking much of that Hoyt talk away from the usual sources.  Sort of a shame since Hoyt finally stepped up speed without going to a 6" brace.  While at the same time honestly improving rigidity and system torque.  I haven't seen a Hoyt this good in decades.  I wonder if folks are just getting tired of the companies arrogance, if they've finally realized fit and finish does matter for that much money or if they just hate that new limb and vibra-slapper

[lamrith]

Wow Rad, awesome info as usual  Thanks!!
So a question to follow up.  Could ask PM, but figure others can learn from it...

Given the choice If you can maintain proper spine and FOC do you favor a heavier slower arrow or a faster lighter arrow within Legal parameters? (6grain/#)

I got a new bow last year, Bowtech Carbon Knight 60#, 30.5" draw. (360grain min legal)
I have 2 different arrows currently

• When I got it I had arrows from my previous bow that still worked.
  Vital Impact 300 (300spine made by GT for Sportsmans WH), AMO length: 30.625, 400grain with 100grain field tip, Std nocks, 11.43FOC
• Then I picked up some of these @ Sportco when they had a sale going ($40/doz).
  Archer Edge 7595 (by GT), AMOlength: 30.625, 415grain with 100grain tip, std nocks, 10.82FOC.

The challenge I ran into was the Vitals shot great with regular nock and FT.  As the season approached I added BH and Nocturnals and things went "sideways"  I had my bow looked at and they did a paper tune got her sending the arrow out cleanly which helped some.  Back home and started tinkering with tip/nock combinations on both arrows. 
The Vital 300's shot better which was the problem I had 4 left when I got the Archers choice and I lost 2 more of them to arrow strikes during practice forcing me to migrate to the Archers choice as the season was starting.
I ended up with a Archers choice that flew pretty well, I revaned with 2" blazes and 3* helical,  This helped drop tail weight and improved FOC marginally, they shot a little better.  They were lower velocity due to a large increase in weight (445grain) to get them to make 11FOC.

Here were the final numbers with nocturnals and 100G BH:

• The Vitals are 407Grain @ 11.63FOC, 292fps over chrono.
• The Archers Choice are 445grain (a +20grain insert weight added to maintain FOC) @11.0FOC, 272fps

I am looking at buying new arrows and relegate the Archers choice to being practice arrows only.  They will be something to send down range and work on consistency with field points without concern about arrow loss.

Do I go with the Vitals again or since even they are well over Min weight do I look for something a bit lighter..  Something to allow me to improve FOC even more with inserts or insert weights if even needed and still be near min weight? (I have GT screw in weights I use for the Archers Choice)  Vitals are really economical ($37/6) but flatter shooting and better FOC is very tempting.  If I could get to ~360-370grain AND 12-15FOC I think that might be the sweet spot and probably put me around 300fps on the nose, KE change is only -2 going lighter and faster.

My thinking is that a faster shooting, higher FOC will be flatter shooting which will be forgiving if ranging errors and better ability to put an arrow thru smaller shot windows as well as being more consistent overall?  Thoughts on spine? 300 or 340?[/list]

[RadSav]

Wow, that was a little confusing.  Are those weights and FOC numbers with Nockturnals and broadheads or without?

[lamrith]

Wow, that was a little confusing.  Are those weights and FOC numbers with Nockturnals and broadheads or without?

Sorry about that Rad.
The last numbers were nockturnals and broadheads.  Early number were original std nocks and field tips.  I added a little to post to clarify..

[RadSav]

I haven't found the Nockturnals to be as accurate as my Easton nocks.  Seems they might stick or push the plunger down at different rates.  So if you are like me that could be some of your inconsistency once you put those on.   Still one of the better ones I've tried though.

I'd say you want the 300 spine at that length.

If you use a range finder the over/under is so minimal at the speed differences you are talking about I wouldn't worry.  Might be a different story if you were guessing yardage on a 3-D course.  But in real hunting conditions it doesn't make a hill of beans worth of difference.  So go with what shoots most accurate and let velocity fall where it may.