Dynamic Spine matching bow?

[Dalton63841]

I have used Stu Miller's Dynamic Spine Calculator A LOT. I still feel unsure how the numbers are working out.

I shoot a 45lb Bear Montana longbow, and I have a 28" draw length, using a BCY X string from 60Xcustom strings. I am told it's on par with a 14 strand fast flight. Those numbers come out to 51.8 for my bow on the calculator.

Now the part that's tripping me up... The only arrows I can find with an appropriate FOC(or under 19% for that matter) are 600 spine arrows that the charts show are for at most a 40lb bow. Is that normal for a cut to center bow?

What are you calling "appropriate" for FOC? Higher is better when it comes to FOC.

Not sure if I am reading your post correctly, but the spine on the calculator will not match what the bow is rated. You want the dynamic sine of the bow to match the dynamic spine of the arrow.

Also, do you have a known well tuned setup put in the calculator, and have your Personal Form Factor set for you? That can make a huge difference.

Bisch

[Dalton63841]

I am aiming for 14-15% FOC, but the best I can do with 500 spine arrows is like 19.5%, and a lot of them approach 21%.

My bow is tuned well at this point. At this point I don't have a reference for the Personal Form Factor I think. My form is good and I can compensate for just about any arrow, but I'm still looking for a set of arrows that shoot WELL out of this bow.

[slowbowjoe]

I would definitely look at .600's of my 45# bows.

[Brock]

I would recommend using calculator to get you in ball park...if you have a setup that works great...as mentioned..enter it into calculator and then adjust the PERSONAL FORM FACTOR until it balances.  Then that number should stay fairly consistent for you on that bow setup for other arrow combos.

I go with heavy heads up front and NEVER pay attention to FOC.  Maybe I am missing it but with a 160, 190 or 200 gr head on the business end of doug fir shafts....that are properly spined for consistent flight.  I never felt the need to wonder if I have good or extreme FOC.

I go by arrow flight and total arrow weight more than measuring FOC.  I just looked an the arrow I shot my huge bear with in June is around 11%....whatever that matters.

There is nothing in the world wrong with 19.5%FOC! If those .500's tune well, then go with them. The arrows I currently shoot (Easton Axis FMJ) are just under 19%. The GT's that I used for years before were over 22%.

As long as your arrow is tuned well the arrow will work just fine. Some folks (like Dr Ed Ashby and me) believe that the higher FOC is an advantage on a well tuned arrow.

Bisch

[Sam McMichael]

I agree with Bisch when he suggests that you go with these arrows since they are tuned well. The actual degree of FOC is less important than they way the arrow performs. Perhaps, though, my opinion is not worth much, because FOC is totally irrelevant to me. I want an arrow that shoots well, period. When you get a pass through, all that extra efficiency just drives the arrow deeper in the dirt on the other side of an animal. Granted, I don't shoot at anything larger than our Georgia sized white tails.

[dbd870]

Why is 19.5% FOC an issue for you. If the arrow flys well use it. My carbon arrows for my 50# recurve have a FOC of 21.5%, high FOC's with carbon arrows are not uncommon.

[Fastltz]

I would never use the information on the arrow box to get you close they tend to be way off. Stus calculator will get you in the ball park. I suggest an arrow test kit then you can try all the spines. Also get a tip test kit. Now as far as foc goes its all personal preference if u want less then aim for less your call. My goal when tuning an arrow is first great flight, second is gpp then lastly is foc. Good luck

[Dalton63841]

Originally posted by dbd870:
Why is 19.5% FOC an issue for you. If the arrow flys well use it. My carbon arrows for my 50# recurve have a FOC of 21.5%, high FOC's with carbon arrows are not uncommon.

19.5% FOC isn't really an issue per se. My biggest problem is I haven't had this bow for TOO long, and I'm pretty poor so I haven't gotten to experiment to find arrows with GOOD flight(so no personal form factor reference). I'm just looking for what will be the best starting point(which I understood was close to matching dynamic spine and FOC between 7 and 15) so that they will actually tune. This is my first cut-TO-center longbow. I'm much more comfortable with recurves.

I've got some 31" Carbon Express 3050's with 175gr tips, and I've got a few 29.5"(the proper length for me) Easton Axis Traditional 400's with the same tips. With either arrow I can hit where I want, because I've shot them enough to compensate for their flight, but neither of them actually hit where I aim.

I have been using both Stu's Calculator(the XML file) and the Dynamic Spine calculator on Three Rivers Archery website.

[old_goat2]

Originally posted by Dalton63841:
 

Originally posted by dbd870:
Why is 19.5% FOC an issue for you. If the arrow flys well use it. My carbon arrows for my 50# recurve have a FOC of 21.5%, high FOC's with carbon arrows are not uncommon.

19.5% FOC isn't really an issue per se. My biggest problem is I haven't had this bow for TOO long, and I'm pretty poor so I haven't gotten to experiment to find arrows with GOOD flight(so no personal form factor reference). I'm just looking for what will be the best starting point(which I understood was close to matching dynamic spine and FOC between 7 and 15) so that they will actually tune. This is my first cut-TO-center longbow. I'm much more comfortable with recurves.

I've got some 31" Carbon Express 3050's with 175gr tips, and I've got a few 29.5"(the proper length for me) Easton Axis Traditional 400's with the same tips. With either arrow I can hit where I want, because I've shot them enough to compensate for their flight, but neither of them actually hit where I aim.

I have been using both Stu's Calculator(the XML file) and the Dynamic Spine calculator on Three Rivers Archery website. [/b]

Try to get out of the mindset of "proper length for me" with arrows and traditional bows. Arrows need to be the length they need to be too be tuned, they do have to be sufficiently long enough if using broadheads that the heads don't hit the riser and pull the arrow off the string. At least that's my opinion!

[Rob DiStefano]

imho ... NO "spine calculator" can ever consistently predict a good arrow spine as there are far too many factors involved, starting with the archer and ending with the arrow's flight past the bow's riser.

i know, i know - many of you are gonna chime in and praise these shaft selection systems as they've nailed for you what you consider the perfect shaft spine for a specific bow and its tasks.  consider yerself lucky - maybe.  you might think otherwise if other shaft brands and spines are tested out.  not all arrows and their spine labels are alike.  

in my experience with all manner of shaft materials, over the last 60 years of messing with all things trad archery/bowhunting, personal testing trumps computer based "smarts" every time.  there simply is no substitute, sorry.  yep, there will usually be both monetary and time costs involved.

carbon shafts have a far higher ratio of static to dynamic spine stiffness.  this ratio is apparent as all carbon shafts list a very wide range of static spine, typically 15 to 20 pounds - you don't see that with wood, alum, alum hybrid or glass shafting.  

that fact alone - the large STATIC spine range - can easily become even wider when DYNAMIC spine is considered.  hence, it's very plausible that a 29" 500 static spine carbon arrow with 350 grains up front can fly very well out of a 55# holding weight bow ... or a 45# holding weight bow.

how you shoot a bow, how that bow is set up, all the parameters of the bowstring, and how your arrow is built, will all play MAJOR roles in how any arrow shaft will react upon your release of the bowstring, and how it will subsequently fly.

at best, shaft selection software is a third party tool that might get you into the ballpark for the arrow criteria you might need for a specific bow and task.  just don't rule out the benefits of seat-of-the-pants testing.  you may be surprised at your results.

[ChuckC]

" I don't always agree with Rob, but when I do, it is about this !"    

( OK, an accent really helps this, at least I have the beard part).      
ChuckC

[katman]

I am also with Rob. Good post.

[dbd870]

My recent project of getting a carbon arrow set up for my Martin finds me agreeing with Rob as well.

[kat]

Good post Rob. You covered what I have been saying all along.

[Dalton63841]

Okay, so effectively the only way to find the right spine arrows for your bow is to buy several sizes and test.

I'm not in a position to do that right now. I can tell that I definitely need a 500-600 spine arrow. The 400 spine arrows I have are obviously stiff. I'm thinking the Carbon Express Predator II 3050's should be a good place to start, and then I should be able to at least get a good tune out of them.

[Rob DiStefano]

there used to be, and may still be, more than a few vendors who offered carbon shaft test kits, or that you could buy 2 or 3 shafts each of a specific static spine.  this would be a good "shaft kit" of sorts to have on hand for testing out any and all current or future bows in your ascham.

[Dalton63841]

Originally posted by Rob DiStefano:
there used to be, and may still be, more than a few vendors who offered carbon shaft test kits, or that you could buy 2 or 3 shafts each of a specific static spine.  this would be a good "shaft kit" of sorts to have on hand for testing out any and all current or future bows in your ascham.

Oh yea I've seen the test kits, but at the moment if I buy a test kit it will be a while before I can buy arrows. When I'm a bit more financially capable, I will definitely look into them, before spending money on good arrows.

[Rob DiStefano]

Originally posted by Dalton63841:
     

Originally posted by Rob DiStefano:
there used to be, and may still be, more than a few vendors who offered carbon shaft test kits, or that you could buy 2 or 3 shafts each of a specific static spine.  this would be a good "shaft kit" of sorts to have on hand for testing out any and all current or future bows in your ascham.

Oh yea I've seen the test kits, but at the moment if I buy a test kit it will be a while before I can buy arrows. When I'm a bit more financially capable, I will definitely look into them, before spending money on good arrows. [/b]

i hear ya.  but at least you could spend time with the test shafts and know what shafting you'll eventually need to acquire.

along with the test kit shafts, it's good to acquire a goodly array of different field point weights.

i usually cut one shaft exactly to my draw length (depth of nock to front of riser shelf, at full draw) + 1/2".  then another shaft at that length + 1 full inch.  fletch each up with whatever i'll use for a hunting arrow (5.25" custom burnt high shield x 3, left wing and full helical), begin testing out different point weights, from 150 through 350 grains.

videoing the test shooting can be a very good thing to do, even if a simple camera/vid is used, then import the video into vid editing software and see how well it captured your release and arrow as it moved to, through, and past the riser, by checking each vid frame.  check it with both a good and not-so-good release.