Hey there...

I was on that bowjackson website checking out figures and whatnot regarding my old PSE bow and the XX75 arrows.

(Butch - stop it... You're old bow is set and is set as good as it's gonna get. Stop messing with it and stop bothering with calculations... You'll hurt your brain....) I can hear you all saying this to me!

Anyway, I read on the internet about finding your arrows true FOC (Front of Center) by balancing it on a nail and dividing the results, subtracting .50 then multiplying to a percentage.

See the image of my arrows below... The top one is an Easton XX75 Camo Hunter with a 125gr Thunderhead. Cutlength: 30.5"

The bottom arrow is also an XX75 Camo Hunter but with my new Magnus Stinger 4 blade 100gr broadhead. Cutlength: 30.5"

Thunderhead: 19" balance point on nail.
19 / 30.5 - .50 * 100 = 12.29 FOC
Total arrow weight: 568 grains

Stinger: 18.5" balance point on nail.
18.5 / 30.5 - .50 * 100 = 10.65 FOC
Total arrow weight: 543 grains

My bow (old PSE 65#, 65% letoff, 30" draw) shoots the Stingers beautifully and so amazingly accurate, I still can't believe how well they fly! I am totally serious... they hit the exact same spot as my 125gr field tips. No tuning needed at all. (Well then again, I did use the spare rubber O-rings from the old box of Thunderheads and used them on the Stingers, so I could align the main blade vertical with the bow string.)

What do you all think of these figures and calculations and stuff? I mean, a 568gr Thunderhead is going to hit like a Mack truck. It does have a teeny bit of drop compared to the 125gr field tips. The 100gr Stingers at 543gr fly beautifully and probably a hair more fps. I wouldguess...

Butch A.

Butch. Repeat after me. If it ain't broke. DON'T fix it.

Yeah, I know, I know, I know....[:-] I just have this weird curiosity thing where I want to know why. But then, I don't have a PHD in physics or mechanical engineering or aerodynamics. How can a 100gr broadhead hit the same spot as a 125gr field tip and still fly perfectly straight with no fishtailing or porposing or whatever?

I think because your arrows are slightly underspined if I recall correctly. And you could probably use some touch up on your tuning.

Just out of curiousity, how does it shoot with 100 grn field tips and 100 grn broad heads? It should be the same. I don't see why you would use on weight for broad heads and another to practice with. That just smacks of something not being right.


Paul

I picked up some 100gr field tips to mess around with. You are correct.... The 100gr field tips shothigh compared to the 125gr field tips (and didn't porpois or fishtale). I bareshaft tested by bow too like you and others mentioned too with a 1/2 trashed XX75 that I cut the fletchings off of.

With a 125gr field tip on a bare shaft from 20 yards, it flew straight with no wobble, porpois, fishtale, and hitthe bottom of the target.

With a 100gr field tip on a bare shaft from 20 yards, it scared me... It flew almost like a corkscrew and was porpoising like a dolphin! [&:] It hit the target on the front edge at an weird angle too.

This experiment told me that my old bow is setup and tuned for2315's cut at 30.5" and 125gr tips, and that's just the way it's gonna be... Why the 100gr Stingers shoot straight and dead on accurate is beyond me. I am going to order some 125gr Slick Tricks now and see what they are like compared to the 125gr Thunderheads.

Why do the 100 gn Stingers shoot with your 125 gn field points? I'll answer that with another old saying: Don't question success.

Got this from somewhere, it is a copy and paste, not law


9% is Ideal forward of Center
here is the most accurate way to determine forward of center...

Get a long finishing nail and nail it into a wall just enough to get it snug without falling out. Now with your finished arrow find the balancing point on the arrow and mark that spot on the arrow.

Measure from the throat of the nock to the end of the shaft ( do not measure the point or insert) this is the cut length of your arrow.

Now, divide this measurement by 2 this will give your center of the arrow measurement.

Mark the center of the arrow (from the throat of the nock to the center).

Measure the distance between the balancing point to the center.

Multiply this measurement by 100 then divide that multiple by the arrows cut length.

This will give you your FOC%

By using the Bowjackson site' calculator my foc was between .59 and .7 lower than using the above chart.

Not for me!

The higher the FOC, the better. That is, until you reach the point where trajectory is affected too much. This becomes a problem with high FOCs when distance is greater. Since my hunting shots are virtually all within 20 yards, trajectory is not much concern. I'd be thrilled to get to the 15%, or higher range.

You will hear me talk about FOC, but to be honest I think it is about the least important factor in arrow flight. The only thing that is important is that you have enough. 9% with adequate fletching on a hunting arrow should work fine. It just forces your fletchings to do thier job is all. Less FOC is a bit harder to tune, but it can be done. Too little FOC and the front of your arrow will try and wander around and with fixed blades the blades will try and steer the arrow instead fo the fletching. I have used as little 7% with small fixed blades they flew well out to 40 yards. I shoot feathers though. It just depends on how good your set up is. Bob Ragsdale thinks it is a bunch of crap and doesn't even concern himself with it from what I can tell.

Butch, I don't think you fully understand what the bares shaft test is and what it tells you. The test you did probably didn't tell you much at all. For starters a bare shaft is very sensitive to form and arrow variations. You should test with really good arrows and more than one. Not a junk arrow that you don't want any more. Chances are that arrow is crap and that's why it didn't fly right. Also you have to shoot more than once. It is process, not a test per say. And I'm confused by your statements. I don't think you did the test correctly to begin with.

You really should have started at 10 yards, it's less scary when the arrow does crazy things like it did with the 100 grn tip. You said the arrow with the 125 tip hit fairly straight but the bottom of the target? Where you aiming at the bottom of the target? The object is to get the bare shafts hitting the same place as the fletched ones and fairly straight. Just like the broad head tuning method. I don't think this is what you were doing? If you get them to group together and the rest is way off from what you think it should be or the arrows are not straight in the target then you most likely have a spine problem or your form is off. I actually like them a bit nock high myself.

What the test you did shows me is that your set up is no where near as good as it could be. And that your fletchings are doing a great job of correcting your arrow flight. Technically the 100 grn should have flown a bit better because it was a stiffer arrow. However you were broad head tuning with the 125 tips so it is set up for the 125 tips. If you change a dynamic on the arrow it will affect how it flies. You would have to re-tune the rest for the changes you made in most cases. The fact that 25 grn less tip weight had that big of an impact though really makes me think your arrows are weak. I think if you had a stiffer arrow the difference would not have been that great. You saw what it did with now fletchings and the 100 grn tip. Imagine what it's doing with the 100 grn broad head on there and how hard the fletchings are having to work to keep it straight. That is why you should not shoot a different weight hunting tip as your practice tip.

That being said, I wouldn't mess with it this close to deer season. I would just go with what you have since you are comfortable with it and it seems to work. You are probably still tuned better than most hunters out there. If you want to play with it wait until next spring when you have more time to dink with it and there is no pressure to rush it.

I will also add that just because you get your bow to bare shaft perfect does not mean your broad heads will still impact exactly the same place as your field tips. It will tell you that your arrows are coming out as straight as they can be though. Broad heads are not the same as field tips so it should not be a shock that they fly slighty different. You could either compensate with your sights or tune your bow to shoot the broad heads in the same place as your field points. It should be pretty darn close to begin with so only very slight adjustments would have to be made.

Check out this link, it is a thread about tuning on AT. One guy describes how he bareshaft tunes, and I describe how I do it. I don't really care for using paper myself. They are two completely different tests and shouldn't be mixed in my opinion. I also list links to Eastons Tuning Guide and Bob Ragsdale's home page farther down the page in that thread. We have talked about it here as well if you search for it. Use the key word "bareshaft" or "bare shaft".

tuning thread

I don't want you to think I am arguing with you or being an ass either. I am just letting you know how I am interpreting things from the way you are describing them.

Good luck,
Paul

You've got to remember that a lot of what Ragsdale has on his Q&A site is very dated material. He doesn't think FOC is a 'bunch of crap'. It's just that when he wrote that, it was awfully difficult to get an arrow set up with a very low FOC. Broadheads under 100 grains were practically unheard of, so there wasn't much need to concern yourself with FOC. Beyond that, remember that his primary emphasis is on TARGET setups, not hunting rigs.

Nowadays, there are a whole bunch of ultralight broadheads and FOC has become an issue. Worst case scenario. Take a 55 grain broadhead and stick it on a 30" 2219, with 5" vanes (a typical WalMart aluminum arrow) you'll wind up with an FOC around 3.5%. That's way too low to get anything close to resembling reasonable arrow flight, especially with a broadhead.

I also question that stuff about 9% being 'optimum.' Don't know who came up with that figure, but it was probably somebody trying to sell something. I won't go any lower than 10% for a broadhead arrow.