Stu's calculator: Advice Please

[USN_Sam1385]

Okay. So here's the deal. I just started using Stu's calculator. Cool program. However, it goes against what many others would advise in this particular situation.

Here is my input information:

GT 5575, 28.5", Point weight: 175 gr., Nock end weight 10 grains, 3 x 4" feathers. The number I get is: Dynamic Spine 77.4

My bow input is 55#, 26" Rated, 28" Your Draw, Fast Flight 16 strand = Dynamic Spine 78.0

Almost perfect right:

Well here is the kicker. My total weight is only 457 grains, and GPP is only 7.4. However if I add a 100 grain brass insert (which I am getting ready to do), it brings the arrow all the way down to 60.8 pounds. However, adding the inserts brings my arrow weight to 557, and gives me 9.1 GPP which is in the range that you guys and the custom bowyer recommended me to be at.

Thoughts?

[JimB]

That is about the same setup I had tuned to a 48# Mojostik.I think you will be underspined with that additional front end weight.

[needcoffee]

I shoot the GT7595 out of a 60# bow. I put on a heavier broadhead and insert combination to move the center of balance and ended up have to foot the arrow with a 6 inch 1/4 oak dowel to get the right dynamic spine via Stu's calculator. Adcock has a "how to" on using a dowel to foot an arrow on his website.  I am relatively new at traditional archery (mostly used wheels up till now).  But I will say the spine calculator seems to work pretty well.  My fletched and unfletched groups are on top of each other.

[scedvm]

I've fought this problem with the GT's as well, they are a pretty light shaft.  At around 60# you could shoot the stiffer 7595's with more front end weight or you might look at the CX Heritage 250's which will tune similarly to the 5575's that you are currently using but are nearly 2gr/inch heavier so your arrow weight will increase 50-60gr right there.  I agree that if your arrows are tuned now adding the brass insert may mess with your flight.  There are weight tubes and a lot of other ways people add weight to shafts without changing spine that you could search on here as well.  Good luck...Shawn

[metsastaja]

Little spooky that Stu's calculator tells you what you have. Been more then a few who have changed arrows after playing with the calculator.

The CE250's come in at 521 with a 175 BH and the standard insert which is about 16g on a 5/16 carbon using your specs.

Before changing arrows.
Make sure you have your center cut correct. If bow is cut to -1/8 don't forget to add in any strike plate thickness you have added.

[hkmp5]

Hello USN_Sam1385,

I think the DSC is giving you good advice.  There are hundreds of arrow setups that will tune to a given bow.  The key to selecting any one of those is based on how you plan to use then.  In your case, the 5575 setup you describe would be a great 3D arrow with a fast, flat trajectory.  For a pure hunting setup I personally would choose something in the 10~11 GPP range with a high FOC% because it would be more stabil in windy conditions and also quieter off the bow.  That means I would go with a stiffer shaft and a heaver point (perhaps even a touch longer than a target arrow)

So, that said, if you would like a heavier arrow select the 7595 and start trying weights and lengths neccessary to keep your dynamic still at 78#.  You will find a good option I am sure.

The other thing you may want to consider is swithing to a shaft that has a higher GPI which will help you keep the point weight down a bit.  (Hint: Wen a shaft is selected you can see all the details of it, like GPI, by looking at the first line of the "Data Library" tab at the bottom of the DSC)

In any case, checking all of these variables at ne time in a quantitative way so that the individual archer can find the "right" arrow for his application is exactly why I made this calculator.  Keep at it and feel free to ask if you run into any roadblocks that we can help with.

-Stu Miller

[BenBow]

You could cut your arrow to 27.5" and build your plate out just a little and be right in the ball park. 548 & 8.9

[xtrema312]

Maybe split the difference and try a 50 gr. insert or 100 and drop point weight.  Try to get over 8 gpp so you are safe shooting the arrow and just see how it flies.  You have the arrows no so why not give it a try?  Then you can build out your side plate a little to make them work.  

I don't know your center cut, but I find bows cut past center shoot a weaker arrow than what the calculator says with a carbon.  I don't know why that is for me, but it is consistent over four bows now.  If my bow is cut to center or out from center, the calculator gets real close, and all I have to do is tweak a little due to my specific bow and shooting form variables.

I would go with the CE250 on a new shaft if you don’t mind the cost.  They act a little stiffer for me than 5575 and you get a lot more weight in just the shaft.  If you want to keep the cost down then try a 340 or 7595 and point weight.

[Huntschool]

Sam:

based on what you showed above I sent you an email with an attachment.

I showed you a GT but I have to agree you might be better off with a CX or a PSE for shaft weight.

[xtrema312]

I have some shafts that run in the low 8 gpp.  Safe to shoot, but my bow is just too loud and vibrates more than I like shooting them.  I added a 3” aluminum footing.  That let me get another 25 gr. on the front.  Total was 55 gr. and the same spine for the arrow so no change to my tune.  That gained me a little more than 1 gpp., made my arrow more durable on stumps.

[doowop]

Install just one insert with hot melt, screw in your point and shoot it. See how it flies.