Excalibur Crossbow Forum

GaryL · Post by **GaryL** » Fri Mar 04, 2005 11:31 am

This is just a simple reminder for those interested in checking there FOC.

FOC as all knows vary with with the bolt or arrow you may be shooting, and really needs to be checked for proper arrow/bolt flight.

You can do a smiple search on the forum here under FOC and see how this is done. Another good site for FOC is Martin Archery and Easton Arrows.

Their are certain guide lines and accepted FOC balance that has proven to work in your advantage.

First measure your bolt or arrow from the tip of your broadhead or field tip to the nock point where nock meets your string, Divide this in half and find the center.

Now take and balance your bolt or arrow on a triangle block or stick a razor blade in a peice of foam and find the balance point and mark it. Measure the distance from your center mark from the length of bolt or arrow to the balance point marked. IE: length of arrow/bolt = 21" center would be 10 1/2"., balance point of bolt = 12"...so take center mark measure to balance mark = 2" Now go here and enter the two measurments and get your FOC... http://home.att.net/~sajackson/archery9.html

The general rule is more FOC for hunting bolts, greater distances group better. If you change your bolts/arrows such as Alum. too carbon, 2216 to 2219 check your FOC and play around with it to see what gives you your best groups at target and hunting distances.

Just a little bit you can do too assure good arrow flight and help tighten your groups.

DOXNUT · Post by **DOXNUT** » Fri Mar 04, 2005 11:41 am

Very Nice, GaryL! I personally feel FOC plays a big part in shooting tight groups.

Easton has a Shaft selection software that provides a kinetic energy calculator and a FOC calculator.

LoneWolf · Post by **LoneWolf** » Fri Mar 04, 2005 1:00 pm

deleted

LW

Quickshot · Post by **Quickshot** » Sat Mar 05, 2005 6:38 am

I use FOC for my compond but have never tested it for my exocet. I get such tight groups now I can't imagin it any better. I've gotten tight groups right from the start, maybe excalibur has already done this when they put the bolts in there kits.
Anyway great info, it is worth checking, thanks for the link.

ExcalBeliever · Post by **ExcalBeliever** » Sat Mar 05, 2005 7:21 am

First measure your bolt or arrow from the tip of your broadhead or field tip......

That is a VERY GOOD point Gary, some research has shown that calculating F.O.C.'s have the measurement to the front insert and NOT the tip of the point.

On BH's that will make a difference...less so on FP's.

Thanks.

Zeke · Post by **Zeke** » Sat Mar 05, 2005 7:45 am

This calculator is fun too:

http://www.goldtip.com/calculators/foc.asp

It's on the GT web site. The cool part is once you got all the figures together for all the components, you can play around with some of the variables like fletching weight and broadhead weight. That allows you to instantly see what changes they will make on FOC.

The real test is in shooting, but the calculators allow you to see where the bolt stands with a given recipe.

Here's what I came up with for the CX CrossBolts:

20" CX Crossbolt - Weight before broadhead
Shaft 13.1 gpi - 262.0gr
Nock - 11.5gr - 11.5gr
Insert - 24.5gr - 24.5gr
Vanes - 11.5gr ea - 34.5gr
--------------------------
Total w/o head - 332.5
w 85 gr head - 417.5 - FOC 9.13%
w 100 gr head - 432.5 - FOC 10.49%
w 125 gr head - 457.5 - FOC 12.54%
w 150 gr head - 482.5 - FOC 14.34%

The CX's are some fat-n-heavy bolts. They are very stiff too. I'm leaning towards ditching them for some Laser II's so I can shoot faster and still have good FOC.

PRB · Post by **PRB** » Sat Mar 05, 2005 8:08 am

I didnt get it exactly perfect but Im coming up with around 12% with a 20" Laser II and a 125 grain Montec. I hope thats good because I sure like the groups Im getting now. Thanks for the info.

Zeke · Post by **Zeke** » Sat Mar 05, 2005 8:08 am

bstout wrote:!3% is good for hunting heads. The heavier FOC really shines when shooting through a high cross wind.

Bob

It was your suggestion that got me playing around with it - I'm kinda using that as my goal FOC - 12 to 13%.

GaryL · Post by **GaryL** » Sat Mar 05, 2005 8:16 am

Zeke that is a good link, however I feel they need to add the total length of the arrow (tip to where string butts against the nock) for a better cal. on balance. By leaving out the length of the tip or broadhead your FOC is leaving out the true measurment of the total shaft.

Zeke · Post by **Zeke** » Sat Mar 05, 2005 8:27 am

OK... 10-4!

wabi · Post by **wabi** » Sat Mar 05, 2005 8:37 am

I used to worry about FOC until I started experimenting with carbons out of my longbow. I needed to add weight to some PSE arrows and added it all at the point. They fly great! Just like darts, literally

FOC = 1.69
Yes 1.69 a 220 grain arrow with a 250 grain point and they fly great.

Zeke · Post by **Zeke** » Sat Mar 05, 2005 8:46 am

wabi wrote:I used to worry about FOC until I started experimenting with carbons out of my longbow. I needed to add weight to some PSE arrows and added it all at the point. They fly great! Just like darts, literally
FOC = 1.69
Yes 1.69 a 220 grain arrow with a 250 grain point and they fly great.

With the amount of experience under your belt wabi, you could probably bit bullseyes with a bamboo skewer at 20 paces!

That is an interesting point though... and to me, it drives home how important it is to try a variety of arrow recipes and find which one shoots well from your bow.

DOXNUT · Post by **DOXNUT** » Sat Mar 05, 2005 10:20 am

For the past few years I have been Using a Laser Bolt (.300 OD)20" 3-5"marco vanes w/R.Helico, 476gr w/125 montec, averaging 300FPS with 16.2% FOC. No complaints so far.

Hoss · Post by **Hoss** » Sat Mar 05, 2005 1:55 pm

GaryL wrote:
The general rule is more FOC for hunting bolts, greater distances group better. If you change your bolts/arrows such as Alum. too carbon, 2216 to 2219 check your FOC and play around with it to see what gives you your best groups at target and hunting distances.

Gary you say more FOC for hunting that gives better down range or long shot groups..ok my question is to what point is more FOC stop...or is there a point where there is to much FOC, Im sure there is but I was curious if there is a idea ZONE so to speak..and then not to go past that..

I hope you understand what Im askin..

Hoss

GaryL · Post by **GaryL** » Sat Mar 05, 2005 2:36 pm

On a hunting head a idea ZONE so to speak is 12 - 14% depends on which book you might be reading...most claim 12%. On the other hand as long as you did not get it so heavy it fell off your crossbow it would work, might only get 3fps and shoot 3ft but yer group would be tight....

This is what I have read and found in my searches on FOC. I want too tell ya their is a lot on FOC out there

Test and see is the tried and true method that works fer most...My hunting bolts are in the 11% FOC and group good for me out to 40yards, I will only take a 30 - 35 yard shot and most have been at 20 - 25 yards on deer.

I have seen in action and also have read where the FOC is most important on lighter carbon arrows that were grouping good at say 20 yards and started opening up at 30 yards and futher.

FOC

FOC

Re: FOC