3 Rivers Spine Calculator

[JLeMieux]

I'm getting ready to build up some arrows for my AW Tree Stick for 3-D. It's 47# at 28" and I draw about 28.5". I bought some 500's for it and plugged everything into the calculator to get a starting point. According it, 500's are pretty weak. The best I could do would be 29.25" (borderline too short) with aluminum inserts, and a 100 gr point.

No side plate, shooting off the shelf.

Does this sound off to you guys? This would give me a 370 gr arrow roughly. Lighter than I want to shoot.

[3R Shooter]

I'm not too familiar with that bow, but a 500 sounds like a good spine for it. What length are you wanting the arrows to be? I could see a 400 spine if you are wanting them longer and/or add some extra point weight. If you have the time, I always encourage doing a test kit of bare shafts. See what the bow and your shooting style likes for spine.

[Bisch]

Something does not sound right? Does that calculator have an entry for center cut??? I use Stu Millers calculator, and if you don’t have the centercut measurement correct, it will throw the whole thing out of kilter.

All of my bows are 48-50 at my 29” DL, and I don’t know the exact length because they are not my everyday arrow (but they are obviously longer than 29”), the .500’s I have worked up come in right at 500gr. That is with a 75gr insert and a 150gr point/broadhead. I guess the shaft you are using could come into play, as some are much lighter than others. I use Easton FMJ’s, which are on the heavier side.

Bisch

[JLeMieux]

Thanks fellas, the center cut was preloaded in the calculator but I'm not sure if it is correct. I'm just going to cut it as short as possible and start there. If it is weak and if I'm getting too light on arrow weight, I'll move to a stiffer arrow.

[Neukdae]

Thanks fellas, the center cut was preloaded in the calculator but I'm not sure if it is correct. I'm just going to cut it as short as possible and start there. If it is weak and if I'm getting too light on arrow weight, I'll move to a stiffer arrow.

The center cut should be correct if you chose the correct bow (3 rivers has the centercuts for all the bows in the list pre measured), however if you have a strikeplate that needs to be taken into account so that you have the true "centercut".

[JLeMieux]

I did end up adding 1/8" for a strike plate and just shooting a bare shaft the calculator is actually pretty close. I'll fletch some up this afternoon to try. Arrow is a little too light for my liking, even for just a 3-d setup. I'll probably bump up to a 400 spine.

[M60gunner]

Good you know now what’s goin on. Hope it works out. I have had issues getting the correct arrow for my lower weight bow (42#)@28. I ended up going to aluminums to save some frustration.

[McDave]

I don’t think it will be as weak as you think it will be.  If you use a 125 grain point instead of a 100 grain point, that will kick the gpp up over 8, which should be ideal for 3D.  At that point I wouldn’t rely on spine calculators anymore, and bare shaft tune instead.