Just another spine calc. question

[Biggamefish]

I was looking at a couple threads here and got into the three rivers spine calc.  so I put in my info and I get 60.3 dynamic spine (bow) and 36.2 dynamic spine (arrow).  I have good flight so I am not overly concerned but I figure I am doing something majorly wrong with the calculator.  I am shooting a gold tip trad. 32" 5575 100 grn brass insert 175grn point. 5" feathers.  Bow is 50lb@29" and I draw 29.5.  What am I missing?

[arrowslinger22]

How's the flight with broadheads?  If the shelf on your bow is cut center or beyond, those arrows should show weak.

[Biggamefish]

The arrows shoot great with broadheads too.  I guess I just can't figure out the calculators.  Everybody says they are a great starting point but I can't figure them out and I figure it is because I am putting somthing in wrong.

[arrowslinger22]

I misread your first post, thought it was 3555.  Stu's calculator shows about the same numbers as you have.  May be that it's off on certain combinations of weight and shafts.  If the arrows are flying good, must be the calculator.

[Bladepeek]

I just ran the numbers through Stu's calculator and I definitely get weak. Those 5" feathers will cover quite a bit and the carbons recover so fast compared to alum or wood, that they may very well be quite weak and it just isn't showing up. I even changed some things (center cut, bow make) and, while results changed a little, it still showed way weak. I've never seen the calculator be far off. I'd still bet they are weak.

It would be fun, just to experiment, to try it with 110 gr points. Bet they fly well too. Those shafts are pretty forgiving.

[Caughtandhobble]

The calculators are just a starting point. Your arrows may fly great for you. I shoot near the same exact setup 51# longbow, 32.5" GT with a total of 175 grains up front. My arrows bare shaft tune perfect... Your setup does seem rather weak to me, but if it works for you go with.  

[kevsuperg]

i have used the calculator too and with my set up. 45#@28" 3555 29 1/4" 3x5 feathers and 300 gr up front it shows me to be way too weak.  bow 54.4 arrow around 32.  however with these arrows it takes that much weight to get perfect flight. i have tried all the combinations of FPs, 300 grs wins everytime.  
 i dont sweat it.  it is what it is.

Are you sure you have the center cut number correct? (i've never used 3Rivers calculaor but I assume there is an entry for centercut measurement, like on Stu Miller's calculator)?

Your setup is very close to mine and Stu's calculator puts my numbers (bow and arrow) almost exact after I got the personal form factor adjusted correctly.

Bisch

[Biggamefish]

I bare shaft tuned these and got great groups all close and shooting straight.  

  Bish How does the personal form factor work?  Three rivers one has that also but I didn't see an explanation for the numbers?

[Orion]

Matt:  Why worry about it.  If your arrows shoot good, just go with it.  I don't use the calculator, but from what I know about carbons, I think the 55/75 shafts you picked are the right size for your bow weight, arrow weight/point weight and draw length.

The calculator is a work in progress that will get more accurate as more data is incorporated/tested.  Of course, not everyone interprets some of the inputs the same way, and some are just hard to measure.

Regardless, good arrow flight trumps everything else, and you apparently already have it.  

The personal form factor "fudges" the calculator to make known good setups work. It goes from -15 to +15. I took my setup, which is a Sarrels RD longbow and 50# at my 29.5"DL, and the GT55/75 arrow that I KNOW is tuned right thru paper tuning, and entered it in the calculator. It was off a bit(but I don't remember how much because that was a while ago). I played with the personal form factor until the bow and the arrow numbers matched (for me that was -15). Now anytime I enter different arrow combinations into the calculator (as long as my PFF is set to -15) the results are always very close to correct, with only very minor fine tuning required to make them perfect.

Bisch

[kat]

I am shooting a .400 deflection carbon shaft at 32" long with a 30" draw. I am drawing 52#'s with a 100 grain insert and 175 gr. point. The center cut is 3/16" past center.  
I am getting good arrow flight, but could never get the calculators to come close.

[Biggamefish]

Yeah I am not going to change anything that is for sure.  Thanks for all the info.