I hear this all the time and I understand that you want the weight to be forward.. but what really are folks looking for? Is there a formula? Thanks.
If the weight was in the ROC, the arrow would try to turn around in the air. I cant imagine that being very prductive, and the deer, or whatever, would be pretty mad that you just slapped him/her with an arrow. Funny, but not good.
Here is a link to a pretty good explanation of FOC. http://www.huntersfriend.com/2007-Carbon-Arrows/arrow-selection-guide4.htm
Sorry...i put this up at the same time mechdoc did... Front of Center Balance If you've ever played a friendly game of darts, you've surely noticed that the dart is designed so that it's heavy in the front, and light in the back. If the dart were weighted the opposite way, with the tail being heavier than the tip, it would literally spin around and hit the target tail-first. Obviously the ballistics of a dart and an arrow are a bit different, but the underlying concept is similar. A projectile's flight is most stable when most of the projectile's mass is positioned Front (or Forward) of Center [FOC]. As such, an arrow should be heavier in the front than in the back. But how much? Where's the "perfect" balance point? This is another hotly debated issue among archery enthusiasts. Some claim that FOC makes little or no difference, others swear that FOC has a profound effect on accuracy. Even the industry experts don't seem to agree, as the ballistic physics for FOC include some rather elastic variables that make finding an "mathematically optimal" FOC very difficult to declare and prove. To make matters worse, we even see a variation in how FOC itself is calculated, depending upon which "expert" you ask. So while we have no interest in the fine points of the debate, we will agree that the tricky issue of FOC is at least worth considering when purchasing a new set of arrows. With all that said, it is generally believed that an arrow with a high FOC will fly well, but with premature loss of trajectory (nose-diving). While an arrow with a low FOC will hold it's trajectory better, but it will fly erratically. So again, another trade-off for you to consider. While there doesn't seem to be a magic number to aim for, it is generally agreed that the optimal FOC balance for an arrow is somewhere between 7% and 15%. In the example on the left, the 30" long arrow has balance point that is 3" forward of the arrow's actual center (15"). So it's FOC is 3/30 or 10% - a reasonable FOC balance. So when you order your custom arrows, keep FOC in mind. If you choose heavy 5" vanes and an anorexic 50 grain tip, you'll likely have an FOC that is too low. On the other hand, if you choose 3" lightweight feathers and a jumbo 175 grain tip, you'll likely have too much FOC. Choose an arrow setup that will give you an FOC balance of roughly 7-15%. FOC Calculators: To find the approximate FOC balance of your finished arrow, simply balance your arrow on some kind of fulcrum such that the arrow sits on it's own without tipping forward or backward. Mark this position on the arrow where it balances perfectly. Then measure the entire arrow (from the crotch of the nock to the end of the point), divide the arrow length by 2, and make a mark that indicates the exact center of the arrow. Now just measure the distance between your marks. If you divide the distance between the marks by the total arrow length, then multiply the result by 100, you'll have a reasonable estimate of your arrow's FOC percentage. There are also a number of FOC calculators available online. Here is a sample of one FOC calculator, a simple program to help you predict the FOC balance of your custom arrows. This particular calculator uses 2003 Gold Tip specifications, but the concept is the same regardless of which brand of arrow you ultimately choose. We suggest you take a little time to experiment with the calculator, and learn how each variable affects FOC balance. The 4 boxes highlighted in green must be used. The other boxes, though functional, represent custom options not commonly used. For the purposes of this exercise, you can just ignore grayed-out boxes.
GMMAT...it blows my mind that you had a FOC of less than 1....what kind of vanes did you shoot??? What youu are stating is that the front of your arrow 'basically' weighed the same as the back.....i'm curious of the arrow set up you were using....
With an indoor set-up (Vegas, 5-Spot, etc), it is also beneficial to increase FOC. RJ speaks of this all of the time....heck, some of the fatter GoldTips are spined so stiff you almost are required to put a heavy (over 150-200 grain isn't all too uncommon) tip to get these puppies to fly right. For strictly indoor arrows, I say as much weight as you can put on the tip with some large 4" feathers in the back will serve you best.
As long as there is more weight on the front half than the back, they'll fly. Higher FOC will gain you better penetration, momentum and stability though. Jeff I'm not surprised they flew fine.....Low FOC will be more affected by wind and yes......If you're shooting a fixed blade BH I can't see they would work at all. The closer you get to "even" the more stabilization is required. Correct me if I'm wrong, but weren't you shooting feathers on those? I may be mistaken there.... Physics says that an object (arrow) will fly heavy end forward. So, if you have more weight on the tail than the tip, the arrow would literally flip over in flight and fly nock forward. You may be able to get away with some grains heavier on the back, but I'm not gonna be the one to do the testing to find out how much is too much. So, having said that, the closer to "even" your arrow is balanced the harder the fletching has to "work" to stabilize the arrow.
When figuring the FOC, when you measure your arrow do you measure to the tip of your f/p or broadhead or to where the insert goes in the shaft on my aluminum arrow? I've never tried figuring this out before.
Wow thanks for all the info. I tried the calculator (I'm using Easton Lightspeed 500's not GT shafts). I'm getting 16.7 without a lighted nock (adds 12gr). 14.5% With the lighted nock. That's interesting because my arrows with the lighted nock do better for me than my ones without. Particularly with a big muzzy on the front. There must be something to this. Too much FOC may not be a good thing?
At 16.7% and 14.5% it probably makes no difference but perhaps the extra 12gr tips the scale arrow weight-wise and the tiny bit of extra momentum makes the difference. At your DW and arrow speed, momentum would be a bigger difference maker than FOC, IMO.
If any of you has a lot of time for reading, these articles by Dr. Ashby are very informative. You can learn a great deal about KE, Momentum, Arrow Penetration, Broadhead effectiveness and much, much more. http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=forum;f=24
I read some of Ashby's stuff some time ago. That's why I try to keep my arrow fairly heavy. I can tell you that in bowfishing, momentum wins over speed in an obvious way. (on the other hand, I found no advantage in my hunting situations in using a 2-blade head. Maybe when I go to Africa.) My arrows are 368 grs with the lighted nock. I'm pulling 41 or 43 lbs depending on which bow I'm shooting. I was thinking that the extra 12grs on the lighted nock helped because it helped weaken the spine on my 500's. (which I believe are fairly overspined for my bow)
Weight on the backend will stiffen the spine and perhaps that is what is helping. Anyway, if it helps you may as well use it like that :d
No. Unless you're shooting really long arrows with really heavy points....500's should be perfectly fine.
I have a 26" draw but my shafts are cut to 28.25" They're 30" long with a nock and field point on 'em. I use 125 gr points. I thought the longer length and heavier point weakened spine? Am I totally backward on that??
They may be a better nock, allowing for a cleaner release off of the string. And, as was mentioned....just a tad stiffer which could also be helping. But to be honest, I'm surprised 12 grains made a 2% difference in FOC. I would bet it's a better nock.
