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FOC mystery

Old 04-10-2008, 02:39 AM
  #1  
Spike
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Default FOC mystery

Hi all,

Just measured the FOC of my 20" 2216 arrows, and was shocked to find it's only 5% with 100grain broadheadand overall weight of 426 grains. 125gr field point made only 9%.

I read here about 18% and 20% FOCs, with arrows of the like. What's wrong with me?

My nocks and inserts are plastic. 5" vanes, and no painting but the factory anodizing.

Should I be at all concerned with my low FOC?
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Old 04-10-2008, 07:27 AM
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Default RE: FOC mystery

"Should I be at all concerned with my low FOC?"
Only if you have accuracy problems. If your arrows don't consistnaly shoot to the same point, it may be time to address FOC, like weighted inserts and smaller vanes.
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Old 04-10-2008, 07:42 AM
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Default RE: FOC mystery

There is some good info on the issue here: http://www.excaliburcrossbow.com/php...ic.php?t=21677
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Old 04-10-2008, 10:45 AM
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KLS
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Default RE: FOC mystery

ORIGINAL: lyuv

Hi all,

Just measured the FOC of my 20" 2216 arrows, and was shocked to find it's only 5% with 100grain broadheadand overall weight of 426 grains. 125gr field point made only 9%.

I read here about 18% and 20% FOCs, with arrows of the like. What's wrong with me?

My nocks and inserts are plastic. 5" vanes, and no painting but the factory anodizing.

Should I be at all concerned with my low FOC?


FOC will help with broadhead flight and planing, in fact I had a major change of opinion about NAP 125gr thunderheads from they're performance in my "before setup" to my higher FOC setup, IMO they're picky of arrow setup(and FOC weight), and they went from scattering all overto grouping within a 2" circle by increasing FOC


I have some 2216's I upped the FOC on, 2216's are a fairly heavy shaft in themselves to try to up the FOC, I used 12gr nocks, feathers(which saves about 22gr), weighted inserts and 125gr tips and came up with 445gr and 16%FOC
the rear of my arrows are set up as light as they can get and unfortunately there really isnt any other way toup FOCmore but to add more weight to the tip

I found that 2213's work out pretty well as far as what I wanted for a weight/FOC ratio, mine came out to around 435gr and 18%FOC, however Ifound no real difference in POI or other performance between the 2216's and 2213's out to 40 yards, so, as I've always believed anyway, the extra weight isnt(and really shouldnt be)a big concern...


its hard to find weighted inserts for alumin arrows, I have access to the equipment so I actually made my own, but Ialso came up with an easy DIY for adding insert weight that works good and doesnt require any special tools
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Old 04-11-2008, 10:38 PM
  #5  
Giant Nontypical
 
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Default RE: FOC mystery

if your arrows alumin are over 400 grs and shoot fine,only reason i would up the weight is if i thought it would be too light for bow and cause limb damage..

as KLS said, get 125 points,alumium front insert, go to 2 inch blazer vanes.

me, i stayed with 100 gr points but did change to 2 inch vanes and aluminum inserts.

crossbow guy matthius in italy has tungsten inserts that will take you up to 500 grs,you just glue them in and you are ready to go.


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Old 04-12-2008, 08:44 AM
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Default RE: FOC mystery

KLS...You noted in your post that you had a simple way of adding weight to your arrows to move the FOC forward that didn't require special tools. Would you mind sharing that with us? Thanks, Tom
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Old 04-12-2008, 11:12 AM
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Default RE: FOC mystery

I've done some FOC experiments. I started off w/ stock Excal GT's w/ alum inserts, 5" vanes, they weighed about 357 gr. My choice today is same shafts and nocks, but brass inserts and 4" vanes for a total weight of about 431 gr. w/ about 19% FOC compared to about 10-11% on lighter version. I also used 8-32 tpi threaded stock [steel: 1"= 25 gr]. All w/ 100 gr points/bheads

The easiest way, imho, to add FOC is to simply use a heavier head. The alum inserts weigh about 32 gr, the brass 111 gr, say 80 gr diff. If you try a 170 gr point on alum insert carbons, you will be very close to what I have, w/in 10 gr. You can add a piece of 8-32 like a set screw w/ allen wrench to back of insert to make up or exceed the 10 gr. Use blue loc-tite on it, let set a day or two and then chase the threads to clean out excess loc-tite w/ a 8-32 bottoming tap. I believe their are other weights available between 170 and 100 gr, think there is a 150 gr out there.

Once I got to the 431 gr GT's, w/ 100 gr Slick Teicks, I pretty much hung up the experimenting, but am going to re-try the 2" Blazers w/ bheads and see if I can get same poi as field tips like I do w/ 4" vanes.

Sprouls advice to read on Matthias 72 tests on Italian xbow site is good, he's taken all of this to new levels and has some good data there.

One more note about the GT Lazar II's. Back in 2004 and 05, both Excal and 10 pt were using them. They seemed to have the least run-out of the carbons, had at the time tighter tolerances than the rest THAT I WAS AWARE of, and I've had great luck w/ them compared to the others [by no means all] that I've shot. not too happy w/ the move to Mexico, and somewhere along the line I've gotten some that have an o.d. on the shaft .007" smaller, lol, but got too many of them to look for new now.
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Old 04-12-2008, 01:14 PM
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KLS
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Default RE: FOC mystery

ORIGINAL: TRG3

KLS...You noted in your post that you had a simple way of adding weight to your arrows to move the FOC forward that didn't require special tools. Would you mind sharing that with us? Thanks, Tom


Not at all

as far as alumin arrows I use an insert for the arrow being usedand lead, specifically .22 long rifle bullets

First I take an extra insert, chuck it in a drill and take the collar off with a file, then I drill the insert out as far to the bottom as you can without going through with a bit that lets the bullet side down but is still fairly snug(I cant remember off the top of my head the exact size I used), I then use a small flat head punch and hammer to "set" the bullets inside the insert one on top of the other, then I hotmelt glue the weighted insert behind the regular insert with the lead end of the insert forward
using a lead filled insert is more "solid" IMO and keeps the weight centered in the shaft, plus you don’t have to "find" something that fits doing it this way, you only need to use the appropriate insertto make it work

Theres other alternatives to bullets, including sinkers, lead shot/silicone, ect., but .22LR bullets seem almost made for doing this, they’re simple to make work and work great because they’re soft unjacketed "lead" that’s easy to reform/shape and are just the right dia. to fit into an insert, two of them weigh around 80gr, plus around 25gr(2213) for the insert should get you around a 100gr weighted insert which you can cut down(and/or only use one bullet) to any weight you want depending on what you want for weight and/or your tip weight …
I use mine full length in my 2213's because I use 85gr thunderheads, my weighted inserts are 95gr, plus 110gr for regular insert/tip gives me an OA weight of around 205gr, a 125gr tip with a standard 25gr insert is 150gr so even with 85gr tips I’m still 55gr more front heavy than the basic 125gr tip setup, and like I saidthe 2213 shaftsare IMO just right weight-wise for doing this, my 2213’s ended up right in the area I wanted them as far as weight(435gr) and FOC(18%)

when keeping in mind that the further out toward the end of the arrow you add the weight the less weight is actually needed to improve FOC putting the weight behind the insert isnt the most efficent way, adding a heavier tip would be the best and most efficent way, but other than making custom inserts there really isntmany options with alumin arrows, the added weight needed to equal the couple inches of weight placement differencefrom behindto in front of the insert really doesnt amount to much anyway andits not worth worring about IMO

I make my own inserts on a machine too but actually prefer doing it with an existing insert/lead, its alot easier(I can make one in just a few minutes), they work just as good, it doesnt require any special tools, and I can do it in my house sitting in front of the TV instead of driving around and sitting in the shop listening to a machine run for hours and making up new swear words because I screw up every other insert…


the inserts for my beman thunderbolts are even better yet, thunderbolt/powerbolt inserts are longer and heavier than normal inserts and the rear half of the insert is just added weight(they weigh 45gr if I remember right), you can drill out the back half of the insert and add a .22 bullet to the back of the insert itself, no seperate insert needed,mybeman insertsweight around 75gr and to look at them you cant tell the difference between a stock one and my modified ones


for those who were curious anyway...


this is just one way though and like awshucks' theres a lot of other ideas floating around too that people have come up with for adding front end weight
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Old 04-12-2008, 07:37 PM
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Default RE: FOC mystery

Thanks for the information on adjusting the FOC. Being a muzzleloader, I have access to lots of lead and moulds, so I can fiddle around with your suggestions to fine tune my arrows. Tom
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Old 04-13-2008, 07:58 PM
  #10  
Giant Nontypical
 
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Default RE: FOC mystery

there is a archery shop making points up to 250 grs,hunting and field.
i talked to owner but for life of me i cant remember his name.

his points are fixed hunting points not expanding type.


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