FOC vs. Trajectory...

[Trad-Man]

The question on the table is this...

If I increase my FOC but keep my mass weight the same what can I expect for differences (if any) in trajectory.  Let's say...out to 20 yards.

[Pete McMiller]

No difference.  If your weight stays the same, gravity doesn't care if you have high FOC or not.  In fact, I have been surprised at how little an effect an increase of 150-200 grains has on trajectory out to 25 yards.  Beyond 25 it shows up as quite a bit though.

[dragonheart]

The balistic coeffiecient vs. the amount of flex + the time of arch in flight may lead to a drop of 1-2 inches based on the flex vs. the weight ratio gained in the amount of time and energy used in perportion to the bow weight. LOL!!!

Any other ideas!

[BobCo 1965]

I believe FOC does have something to do with flight trajectory.

I believe that Adcock proved that with his flight records with high FOC.

I don't think you'll see any trajectory differences at 20 yards though.

[Friend]

[Jason R. Wesbrock]

BobCo,

If I'm not mistaken, Larry Hatfield beat at least some of those records with extremely low FOC flight arrows. That's the thing about flight records, they seem the be set and reset every year or two.

In answer to the original question: none.

[Friend]

I have contemplated this in the past since my bare shaft Ultra-EFOC arrows kick once then disappear as my compromised eye site can no longer follow them down range.  Note: I can still easily follow a normal FOC arrow down range.  I posed this similar question to Dr. Ashby several months again due to my observations. We were both on the same page.

I do notice a difference in trajectory between such arrows.  At ~40 yards, the Ultra-EFOC (32% actual) arrow's drop was ~8-10 inches less than a matching, normal FOC arrow.  Haven’t tried to discern any difference at 20 yards and should have.  I wish now I had retained that same normal FOC arrow for 20 yard testing.  It became another project subject.

My limited observations revealed there was a significant trajectory impact at down range distances. Still would like to pursue Ultra-EFOC trajectory impact at personal hunting ranges. Would suspect possibly a ~1" difference at 20 yards. My shooting skills will have to be up to snuff in order to discern a possible difference.

The higher the FOC the faster the arrow's flight stabilizes, making the arrow much harder to see in flight. That should also mean less arrow energy loss to paradox, and more saved for arrow velocity. I also find that the higher the FOC the more forgiving of modest point weight changes the carbon shafts become.

Hope that helped,

[Bjorn]

Out to 20 yds no change.

[McDave]

If I increase my FOC but keep my mass weight the same what can I expect for differences (if any) in trajectory. Let's say...out to 20 yards.

I agree with previous responses: probably no difference in trajectory out to 20 yards, so far as hunting accuracy is concerned.  I'm sure that if you were in competition shooting at silver dollar sized targets at 20 yards, you would notice a difference, but the arrows should still be in the same 6" circle.

But to take the original question one step further, if you increase the point weight, won't you have to increase the spine of the arrow to compensate, assuming your original setup was properly tuned for your bow?  And won't that be hard to do, since you're reducing the shaft weight behind the point enough to compensate for the increased point weight?

[JimB]

McDave,it can be done if you can find a lighter but stiffer shaft than you are currently using.An example would be switching from a GT that was almost 8+ gpi to a Victory V Force that was a stiffer spine but 6+ gpi.Not too easy to do if you are shooting 10 gpp though.If your current setup was 12-14 gpp,it can be done.

I also agree,I don't think you could see a trajectory difference at 20.

[SlowBowinMO]

Yep, none.  A 650 grain arrow with 30% FOC will not drop one bit faster than a 650 grain arrow with 10% FOC, assuming all else is equal.

The much heavier point does often require a tuning adjustment though, many times the nock point will need to be moved down just a hair to regain proper tune with the heavy point.  Failure to make that little tuning adjustment can add to the perception the high FOC arrows are dropping faster.

[BobCo 1965]

Interesting, thanks Jason.

[Overspined]

I have a tough time with high FOC and carbons from my Hill bows. I use woods and heavy points, but carbons have been tough to get perfectly tuned for me. I think the lack of center shot causes it to be more touchy.

[Trad-Man]

Okay...first of all I do not understand why this thread was moved from "shooting" to "pow wow"...isn't this about shootin?

Since my post this AM I've made some calls and actually turned on my brain...it dosen't always respond...but it's at least on!

In short gents...you are all right on the mark.  

Thank you....

The trajectory vs FOC at a given Mass without my brain on was counter intuitive with my brain off...as Pete stated...gravity dosen't care.

Everybodies experiences are right on from what I have learned since this AM.

McDave...good qustion....yes you would.  Guys are footing the skinny carbons with aluminum and the woody fellas would have to be using a longer piece of a hard footing with an appropiate back half.  In either case your are moving the "bend" forward in the shaft stiffening up the spine vs the total weight.

I know with my tappered carbons (Arrow Dynamics) the "bend/flex" in the shaft takes place about an inch into where the shaft begins to taper which is ~10 inches from the front..not in the center.

All this interest on my end stems from the recent Ashby bone penetration threshold reports.  Why pull more than you have to when you can increase performance by modification to your arrow set-up?

Thanks agin!

-peace
TM

[tg2nd]

My wife's shooting a 45#@24" Hybridbow. She shoots Raminarrows with 100grain pointweight, total arrow weight 450grain and also 2016 Aluminiumarrows with 100grain Brassinsert and 125grain pointweight, total weight 5oograin and also GT Exped. Hunter 3555 with a 100grain brassinsert, 250grain pointweight, total weight 570grain. Out of 23yards there's a noticeable difference. Flattest trajectory: GT 3555 then 2016 alum then ramin arrows.
We changed one GT to a 50grain brass insert and 300grain pointweight (after shortening the shaft 0,5"),almost the same weight (4grains less), but a flatter trajectory.
I think the higher the FOC (keeping the same total arrow weight) the flatter the trajectory.

[Friend]

A decent indicator to further validate some of these findings would be to chrony the same wt Normal FOC and Ultra-EFOC arrows at 20 yards; And various yardages.

Would likely take over 11 fps difference at 20 yards to discern a difference. Of course there are those, that would relish the opportunity to pursue a bow with much less of performance increase.