FOC, Arrow Weight, or Speed?

Please see end of article for an update!

This season the interwebs has been abuzz with talk on what is better for bowhunting. EFOC (Extreme Front of Centre) arrow balance, Heavy arrows for better penetration or Higher speed for a better chance to hit the animal before it moves. It seems though that one thing our international cousins want is ultimate penetration – if you hit bone, it must go through, and anything but a total pass through seems to be a complete failure. KE (Kenetic Energy) is a myth and cannot be trusted…

My own ideas (and the legal requirements) on the matter aside, I thought I would try and devise a basic test to see what I can get out of my setup. Simply build my standard arrow, a heavy arrow with very little FOC, and an arrow of the same weight with a heavy FOC. Shoot them into a new broadhead butt at 10yds, 20yds, 30yds and 40yds and measure the average penetration to see which transfers it’s “benefit” best into the butt. Really simple…

…not so simple.

As soon as you change one parameter, EVERYTHING changes. Heavier arrows are generally stiffer in spine, changing shaft diameters help, but then you don’t have consistency in how much the target medium “grabs” onto the shaft. Heavier field tips are thicker and so on and so forth. The problems seemed unsolvable to get a way to scientifically test, so I simply decided to redneck test it and let you make the conclusions by yourself. I used what most people would be able to get from the rack of their bow shop.

In the end, I built three arrow sets, using GoldTip Kinetic 300 spine shafts. I used the Kinetic arrows because they are thinner, hoping to reduce the effect of the target on the shaft. I also used GrizzlyStick Test Field points as they all had the same outside diameter. The 300 spine was to reduce the effect of spine as best I could with the excessive weights and inserts. This is what I ended up with:


Arrow one – Orange
Arrow Two – Green Arrow Three – Purple
GoldTip Kinetic300 with standard components and a 125gr field point.
Weight: 494gr
Speed: 275fps
KE: 83ft/lbs
Momentum: 0.603slug-ft/sec
FOC: 12%
GoldTip Kinetic300 with heavy weight components + F.A.C.T. Weight inserts + 200gr Field Point.
Weight: 692gr
Speed: 234fps
KE: 84.2ft/lbs
Momentum: 0.718slug-ft/sec
FOC: 18%
GoldTip Kinetic300 with standard component inserts plus a full shaft lengt insert to get the weight balance with a 100gr field point.
Weight: 688gr
Speed: 236fps
KE: 85.1ft/lbs
Momentum: 0.720slug-ft/sec
FOC: 5%

My Testing bow was the Bowtech BT-Mag that I have been hunting with this year. It was still on my last setup settings, 68lbs Draw, Comfort Setting. I wondered about maxing out the performance, but wasn’t sure it would make much of a difference except to make the recorded numbers higher. The difference in percentage points should be very similar, so I decided to leave it. This is where I would hunt in any case.

The Actual Testing
I started with a new broadhead butt to reduce variations as the arrow penetrated through previously damaged areas, rotating it to new positions the whole time to get some kind of consistency in results. All the arrows were shot to the same face (assuming the density would be more or less similar) and shot ten times per distance (10, 20, 30 and 40 yards) to get a good average (highest and lowest removed to even out the results even more)

And this is the surprising FOC result I ended up with:

Green Arrow – 18% FOC: 20.72cm penetration
Purple Arrow – 5% FOC: 21.81cm penetration
Orange Arrow – 12% FOC: 22.33cm penetration

I honestly expected the ExtremeFOC, 18% FOC arrow to have the best penetration, because it had both the weight and the FOC to its benefit. On longer distances (30yds+) the 18%FOC arrow out performed the 5%FOC arrow on penetration, but the 12% (and 200gr lighter arrow) outperformed both?!? But realistically… is a 16mm difference actually worth commenting on?

As far as accuracy and the fabled forgiveness factor came in, the Orange arrow was hands down the winner (no surprise there, the bow was tuned for something close to them), with the Green arrow in a very close second. The 5% FOC Purple arrow started floating when the wind came up (although… to be fair, I could only start commenting on it at 40yds… before that, they landed quite close to where I aimed) but you could definitely see a waggle in the arrow which was not noticed in the other two (and interestingly enough, archers on the range commented that the Purple arrow was noisier than the other two…) Personally, I’d always set up for worst case scenario, best result in the worst conditions.

So my conclusion?

Go for accuracy.

On my setup, only a very lucky shot will shatter a solid shoulder bone and reach vitals if my shot is bad. If that is where you hit, even if you had good penetration, you are in for a long walk! If my shot is good, ribs wont stop the arrow (even on a mechanical broadhead) from passing through the vitals and the animal, and there is literally no animal I can afford to hunt that needs more.

The second part is that should you need more penetration from a lower powered setup, go for a sharper angle broadhead, with cut on contact points.

My feeling is that 10-15% FOC is about as much as you need. After that, it seems to be overkill and no real advantage is gained, where you don’t lose more in another area (like arrow speed) than you gain in pass through momentum. Sure, there is a lot to be said for two points bleeding when you need to track an animal, but there is an upper limit required for a pass through – once you are over that limit, the arrow just passes through faster. And yes, Kinetic Energy is not the best way to measure the penetration you will be getting, but it is a very good average indicator that takes most of the big factors into consideration.

The fact of the matter is that your best chance for a success, for a quick and clean kill, is if your bow is tuned for your arrows, and your arrows are tuned for your broadheads, and you can hit a spot when you aim for it, and hopefully know where to aim.

Add with that a little bit of luck, and a good smattering of knowledge about animal behaviour, you are well on your way to good hunt.


Information Update

This article was originally published in the Africa’s Bowhunter Magazine, after which we received a lot of comments about the testing methods, the foam butt as a medium for penetration testing, etc, etc… Some more research followed and we found that our understanding of EFOC was flawed.

Dr Ed Ashby breaks FOC up as follows:

Normal FOC <12%
High FOC 12%-19%
Extreme FOC 19%-30%
Ultra Extreme FOC >30%

Interestingly enough, in a few places (also in the video below) he says that an improvement in penetration via changes in FOC only starts to show above 19% FOC… our test only went to 18%.
(And lucky for me, Dr Ashby also uses foam butts as a basic testing medium) Before you get to EFOC, there is virtually no visual difference in penetration… according to dr Ashby.

So essentially, my conclusion remains the same… getting to an Extreme FOC or UEFOC setup means some major work on your arrows and tuning which may not be worth all the effort and cost (in time and money) on a modern compound bow.

We will definitely revisit this later with much lighter arrows and much heavier points!

About Sean Nel 51 Articles
Sean Nel is a staff shooter for Archer's Edge South Africa, Beestinger, GoldTip, Sureloc and Health Matrix as well as an accredited Archery Instructor with the South African National Archery Association (SANAA)