Arrow spine - calculating backwards?

[HenrikBP]

After some trial and a lot of frustration, I think I've arrived at an arrow that shoots reasonably well for me. Except that in the process I ended up with a lot more point weight than originally planned.

If I use Stu Miller's spine calculator to come up with a spine number for these arrows, and then calculate "backwards" by changing shaft type/deflection and point weight to arrive at the same spine number, will these "new" arrows be close to what I need?

I figure yes, but maybe someone has some experience with this. I realize of course it will only be approximate specs, and will have to be tested and tweaked on the range.

Details:

Morrison ILF recurve w/ glass foam limbs. 45 lbs at my 27" draw length. Shooting 3-under.
Arrows: Carbon Express Blue Streak 250 = 0.413 deflection, cut to 29 5/8" BOP. 50 grain brass insert, 3 x 4" feathers, 5.5" double-dog Onestringer wraps.
Originally 145 grain points, but now up to 200 grain points.

As my form improved - not great but improved     from what it was - my arrows started to fly worse. After a lot of frustration I finally increased point weight and at 200 grain the arrows fly much better.

I could of course stick with what works now, but would like to keep the arrow weight around 450 grains for ~10 GPP

[Zradix]

I'm new to carbons myself but have been looking into it a lot over the last few days.

.413 sounds stiff to me if you want 450 grains total.

I'll bet you'd like these...
  http://www.shop.bigjimsbowcompany.com/BLEMS-Gold-Tip-Carbon-Shafts-Dz-GTBLEMS.htm  

in the .600 spine with 200 grain tip.

[HenrikBP]

Thanks Zradix,

Yes, .413 is probably too stiff a spine for my draw weight and length (20/20 hindsight, right   :D )

But then I think .600 may be too weak a spine. Especiallly with 200 grain+ up front. I'll run it through the spine calculator and see if the numbers add up.

[BigJim]

henrikBP a 1535 with nock, 50 g brass insert at 28.5" should be about 277g. add a 145-175 tip or even 200g and you will be in about the right weight.
For 45lbs and 27" the .600 spine is great medicine. Now You probably have a riser that is cut past center. This would tend to lean twords a stiffer arrow, but then you have a long limb and 17" riser. If your bow is more than 56" long, you will lean back tword a weaker shaft and so on.
Too much importance is put on the affect of the heavier pt. 200 up front is not that heavy on a carbon arrow and pt weight adjustmen is only for fine tuning. You will get more dramatic resluts from adjusting shaft length.
bigjim

[HenrikBP]

Thanks Jim,

Yes, my Morrison 17" riser is cut past center (3/16" I believe), and overall length of my bow is 62".

I got a shaft "test kit" back when I first tried out carbon shafts, and never could get the .500 spine to shoot right. Now I'm thinking it was due to my release at the time (20/20       )

I'll take a look at .600 as well.

Thanks,

Henrik

[HenrikBP]

I ran a few numbers through the calculator.

My bow is listed as needing 69 pounds dynamic spine.

My original arrow calculated out to 62 pounds.

My original arrows with 200 grain point => 51 pounds

A GT 1535 @ 28.5", 50 gr insert plus 200 gr point => 36 pounds

I know the calculator is just a tool to give general ideas, but that seems like a huge range in spine.