Home › Forums › General Archery Discussion › FOC
This topic contains 12 replies, has 8 contributors, and was last updated by Monsterfreak 1 year, 4 months ago.

AuthorPosts

Hi guys,
have not posted for ages but got a question again.
I use FMJ and GoldTip Kinetic pro arrows with 125 BH and the best FOC I can get is 10.5%.
How can I get it closer to 18%? I do not want to use heavier BH.
Thanks!
that a .300 spine?i am shooting GT velocity XT 300 shafts. with 100 gr tips. i added 30 gr of insert weights. i measured almost 14% FOC.
you have enough spine to add insert weights?
What spine, shaft length, vanes, nock etc are you using now? As vash stated above, you could use Gold Tips insert weight system or possibly brass inserts in the Eastons. Not sure what you are using now, I use brass inserts in my Eastons.If your FOC is reasonable (715%), your arrows will function as they should. And don’t assume that the mathematical average (11%) of the recommended 715% range is somehow the best score. It doesn’t work that way. The ballistic physics for FOC include some rather elastic variables that make finding an “mathematically optimal” FOC very difficult to declare and prove. So don’t pull out your scientific calculator on the FOC issue. It’s not necessary. Just choose a reasonable value and move on. Fortunately, most common arrow components tend to yield finished arrows well within the recommended 715% FOC range. The only real danger of slipping off the FOC precipice is if you use really heavy fletching and superlightweight target nibbs, or if you choose small light fletching and a jumbo tip weight (or a heavy brass insert). For common arrows with basic vanes or feathers, aluminum inserts, and 85125 grain tips, chances are your FOC will come out just fine.Pull Shoot ScoreThanks guys.Spine is .300
NAP Quickspin 2″ vanes no wrap
Shaft lenth 28″
GT nocks and insertsThe only option seems to be heavier inserts or weights.
Thanks guys.
Spine is .300
NAP Quickspin 2″ vanes no wrap
Shaft lenth 28″
GT nocks and insertsThe only option seems to be heavier inserts or weights.
I’ve been playing with FOC and inserts for a couple of months now due to shoulder surgery recovery. Didn’t want to buy new arrows so I’ve been adding/subtracting inserts to adapt my arrows to the lower draw weight I’m using.
I believe you can use the Easton brass hit inserts with the FMJ shafts. If so, you can add 5075 grains with the brass inserts. I bought 100 grain brass inserts from ThreeRivers Archery that also fit. (BTW – I’m using Easton Axis Nano shafts).
Remember everything is a tradeoff. You may have to adjust draw weight to match spline of the shaft you’re using after altering the FOC. You’ll be losing speed, but adding momentum.
Lots of variables.Good luck!
How are you calculating FOC … GT method or Easton/AMO method?I calculate your GT Kinetic Pro 300 as 13.5% using the Easton Method with FPs.
I calculate your Easton FMJ 300 as 11.8% FOC using the Easton Method with FPs.You should get about 1/2% FOC greater when calculating with broadheads.
Calculating FOC is the same as calculating GG for Aviation … it isn’t the wizwas, blahblah, some make it out to be. It is a precise science.
The real question is why do you want 18%? If you are concerned about broadhead flight stability, about 12% is all that is needed for broadheads. Anything over 12% is for increased penetration potential … energy lives where the mass is. Penetration Potential above 12% FOC is only needed for Large Game, like Elk or Moose. Based on testing I’ve done, expect about 4% increased penetration potential for every 1% increase in FOC.
However, there are other factors that go into increased penetration potential.
– Shaft diameter. Calculate the crosssectional density and take the ratio.
– Shaft spine. Stiff spine flexes less on impact, hence puts the energy in alignment with the broadhead cutting path.
– Size of broadhead total cut surface, referred to as TCV. TCV is the Total Cut X Depth. Smaller Total Cut penetrates deeper.Generally, I tailor my arrows, weight and FOC and broadhead choice, for the game I’m hunting. Sure, you can shoot rabbits with a .458 Magnum Elephant gun, but why? I shoot Victory VAP 300 V1 w/ 90gr Penetrator Adaptors and 125gr QAD Exodus 1¼” cut broadheads, FFP 360 helical fletch, Bohning Fnock @ 485gr and 18% FOC for Elk. I wouldn’t use this arrow on Deer/Pronghorn. My Deer/Pronghorn arrow is a Victory VForce V1 350, insert + 20 gr weight, Terminal TLock 11/8″ cut broadheads, FFP360 helical fletch, Bohning Fnock @ 397gr and 12% FOC.
You can only do what you can do once you’ve chosen the shaft (gpi). If you can’t get to where you want to be, you’ll have to make a different shaft choice.
How are you calculating FOC … GT method or Easton/AMO method?
I calculate your GT Kinetic Pro 300 as 13.5% using the Easton Method with FPs.
I calculate your Easton FMJ 300 as 11.8% FOC using the Easton Method with FPs.You should get about 1/2% FOC greater when calculating with broadheads.
Calculating FOC is the same as calculating GG for Aviation … it isn’t the wizwas, blahblah, some make it out to be. It is a precise science.
The real question is why do you want 18%? If you are concerned about broadhead flight stability, about 12% is all that is needed for broadheads. Anything over 12% is for increased penetration potential … energy lives where the mass is. Penetration Potential above 12% FOC is only needed for Large Game, like Elk or Moose. Based on testing I’ve done, expect about4% increased penetration potential for every 1% increase in FOC.
However, there are other factors that go into increased penetration potential.
– Shaft diameter. Calculate the crosssectional density and take the ratio.
– Shaft spine. Stiff spine flexes less on impact, hence puts the energy in alignment with the broadhead cutting path.
– Size of broadhead total cut surface, referred to as TCV. TCV is the Total Cut X Depth. Smaller Total Cut penetrates deeper.Generally, I tailor my arrows, weight and FOC and broadhead choice, for the game I’m hunting. Sure, you can shoot rabbits with a .458 Magnum Elephant gun, but why? I shoot Victory VAP 300 V1 w/ 90gr Penetrator Adaptors and 125gr QAD Exodus 1¼” cut broadheads, FFP 360 helical fletch, Bohning Fnock @ 485gr and 18% FOC for Elk. I wouldn’t use this arrow on Deer/Pronghorn. My Deer/Pronghorn arrow is a Victory VForce V1 350, insert + 20 gr weight, Terminal TLock 11/8″ cut broadheads, FFP360 helical fletch, Bohning Fnock @ 397gr and 12% FOC.
You can only do what you can do once you’ve chosen the shaft (gpi). If you can’t get to where you want to be, you’ll have to make a different shaft choice.
I have used the GT FOC cakcukator as well as physically measuring the balance point and then used the formula.
Here in South Africa I get the chance to hunt Kudu, Eland and Blue wildebeest which are large animals, especially Eland.
Dr. Ed Ashby’s research has shown that a higher FOC results in better penetration and that is what I am looking for.Thanks guys.
Spine is .300
NAP Quickspin 2″ vanes no wrap
Shaft lenth 28″
GT nocks and insertsThe only option seems to be heavier inserts or weights.
I’ve been playing with FOC and inserts for a couple of months now due to shoulder surgery recovery. Didn’t want to buy new arrows so I’ve been adding/subtracting inserts to adapt my arrows to the lower draw weight I’m using.
I believe you can use the Easton brass hit inserts with the FMJ shafts. If so, you can add 5075 grains with the brass inserts. I bought 100 grain brass inserts from ThreeRivers Archery that also fit. (BTW – I’m using Easton Axis Nano shafts).
Remember everything is a tradeoff. You may have to adjust draw weight to match spline of the shaft you’re using after altering the FOC. You’ll be losing speed, but adding momentum.
Lots of variables.Good luck!
Thamls, I will be looking to add the brass inserts.
…Based on testing I’ve done, expect about4% increased penetration potential for every 1% increase in FOC. …
Correct the above to read, “Based on testing I’ve done, expect about 2% increase in penetration potential for every 1% increase in FOC above 12% FOC“.
To get highFOC you need a stiff, but light shaft, so that a large percentage of the weight is concentrated on the broadhead. You can either go with heavier broadheads, 180gr or more, or you can chose a shaft that uses an Adapter (40gr to 90gr), or you can use an insert that accepts a modular weight system, or some combination of each.
For example, I shoot a 29″ 618gr Easton 2018 XX75 (12.28 gpi) arrow out of my 60#@28″ recurve. I use a 210gn German Kinetic Silver Flame broadhead, a 19gr insert with 15gr of insert weight added and fletched Helical with three 5″ feathers. This results in a 19% FOC by Easton/AMO calculations. Because the GK SF is so expensive, my ‘finisher’ arrows use the SteelForce African Phathead 190gr with 35gr of insert weights added. You don’t need a quiver full of $30/each broadheads. http://www.germankinetics.com/
I also shoot a 28″ 487gr Victory VAP V1 300 (8.9 gpi) arrow out of my 63#/28″ Monster. I use a 125gr QAD Exodus broadhead, a 90gn Stainless Steel Penetrator adapter, and fletched Helical with three Flex Fletch FFP360 vanes. This results in a 19% FOC.
To get 18% FOC out of the arrows you have, you’ll need at least 270 grains of total point weight for the FMJ (broadhead+insert/adapter+weights), but the Easton FMJ, even with the 75gr brass HIT insert, will require going to a 200gr broadhead. The GT Kinetic 300 using four 20gn F.A.C.T. weights and a 125gr broadhead would be about 18% FOC, but then the shaft spine is on the weak side.
By ruling out going with a heavier broadhead, I just don’t see getting 18% FOC with what you have and keeping the arrow spine acceptable. Alaska Bowunting UFOC arrows and Arrow Dynamics make tapered shafts in the .250″ spine that accept heavy broadheads for highFOC. Plus, the heavier broadheads are designed to impact and split heavy bone. If cost is a concern, check out the SteelForce Phathead SS180.
http://www.steelforce.com/products/phatheads.htmlBrian’s info above is priceless as always.I’ll throw this out for you even though it doesn’t meet your current broadhead weight. I’m using GT Velocity XTs (Vash will approve) in 300 spine cut at 28.375″ carbon to carbon with 2″ helical blazers and GT acculite nocks, GT 100 grain brass insert and 100 grain QAD Exodus for a total arrow weight of 470 grains. My FOC is right near 18% (Easton method) with field points and may be a bit higher with the exodus but I haven’t measured it. OT2 lists me underspined (hunting) if I get much above about 67 lbs draw (29.5″ Magnum), however I am able to shoot them at 70 lbs with excellent results. The GT velocities weigh in at 8.5 gpi in 300 spine so it helps get you that high FOC. Part of your arrow selection has to be what draw weight and arrow velocity your willing to end up with to get the FOC you want on a properly spined setup. One of these days I’ll try out the VAPs but right now this setup is pretty economical for me and keeps my arrow weight about where I want and velocity in the 280 fps range… VAPs have a smaller diameter though…
Hi guys,
have not posted for ages but got a question again.
I use FMJ and GoldTip Kinetic pro arrows with 125 BH and the best FOC I can get is 10.5%.
How can I get it closer to 18%? I do not want to use heavier BH.
Thanks!
https://www.buildyourownarrow.com/arrowreview.html Here is the web site to the Gold Tip arrow building and I used the Kinetic XT 300 and used one of GT 20 gr weight inserts with their accutough insert and a 125 gr head and got 13% FOC. GT recommended I max out at 12%. At the 13% the diagram shows I’m at the front end near the point in FOC. Dr. Ashby also recommend a certain broadhead for best penetration and with a small diameter shaft like the two you were referring too I would think you would kill any of the African antelope.
https://www.buildyourownarrow.com/additionalweight.html If you use the GT Pro Hunter Black 300 cut at 28″ and use the GT brass insert and 125 point you’ll get the 18% FOC you are looking for in your search.
 This reply was modified 1 year, 4 months ago by Bow Drawn.
Thanks for all the great replies guys! Once again I am reminded of why Mathews and their users are such a great place to be at!Methinks the VAP V1 is a good place to start looking for the FOC I am in need of.
Thanks again!

AuthorPosts
You must be logged in to reply to this topic. Click here to log into your account.