Chris, I just took a look at this calculator, but it doens't seems to calculate right. I know for sure that the dynamic spine for my bow is 53lbs, and this calculator gives me a 40 lbs!

I also shoot with GT's with a 100 grains tip and the calculator gives me a arrowspeed of 188 fsp, while I measure always a 173 max. I also don't beleive that all longbows witht he same drawweight offer the same speed. The only thing that seems to be right is the FOC calculation.... So I would recommend that you forget about this calculator...

Here I have a better calculator, it is German, but I recon you'll understand it:

http://www.bogenblog.de/index.php?/pages/spine-rechner.html
I would try the following: see what dynamic spine you get with this calculator.

Then take a GT which is the closest at this. Dont make the mistake of looking at the "spine values, such as 11-35 or 35-55, but use the calculated AMO spines (which you need):

15-35 = 0.600” becomes: 26/0,6 x 1,2115 = 52,5 lbs

35-55 = 0.500” becomes: 26/0,5 x 1,2115 = 63 lbs

55-75 = 0.400” becomes: 26/0,4 x 1,2115 = 78 lbs

75-95 = 0.300” becomes: 26/0,3 x 1,2115 = 105 lbs

I'll give you an example. At my drawlength of 29 inches my R/D longbow delivers a 38.5 pounds. When I use this German calculator, I get an dynamic spine of 53 lbs. When I make my own calculations I end up with pretty much the same. This is because this calculator is based upon the same parameters as I use. If you want to know the exact parameteres, let me know!

Which means I use a Goldtip 15-35! I shoot this arrow with the standard insert at the front, an 100 grains fieldtip and the standard GT nock.

I choose for the 100 grains because intensive bareshafting prooved in a convincing way that this was the right weight.

My FOC is a bit heigh (13 %) , but since I shoot selden over the 60 yrds, this is no problem.

So my advice to you would be to do the same. From what I know from your bow-parameters ( I don't have all info), I would say you need a GT 35-55 with a 110 or 125 grains point. The only way to be sure you have the right bow/arrow combination is to shoot with it! But start with bare-shafting to fine-tune your arrow! I am instructing people here for bowshooting in The Netherlands am writing an booklet about how to tune arrows and this method prooved itself!

Oh yeah and forget the charts of the manufacturers, they really s*ck!