Longbow Spine Calc issues

[Dan A]

I went ahead today and pulled the trigger on a left handed longbow.

I decided to buy a cheap one and just continue practicing while I have a custom built for me which will take a few months or more.

Grabbed a Bear Montana and will pass it down to a kid when I am done with it.

The reputable online dealer I bought it from suggested a 500 spine Axis Trad for it even though their own spine calculator said 600 spine.

I called back and confirmed and again they said, no 600 is underspined for the bow.

I downloaded a spine calculator that was suggested but I am embarrassed to say I am too ignorant to use it. I don't know what all those acronyms stand for.

Also if I am looking at the Easton charts correctly I am also seeing 600 spine there.

Anyways after a few hours of trying to figure this out, I call Uncle and was wondering if someone could help me out and tell me:

What spine
What gr point
Length to have arrows cut

Would be nice if I could use 500 spine as I already have a dozen of those bare shafts laying around but I want it to be as right as possible.

Bow Specs:

Bear Montana
45#
Draw length I am pulling 26.5"
Strings: D97 Flemish

Arrow:

Easton Axis Traditional
Feathers 3x5" parabolic
Insert weight 16 gr.
Nock weight 9 gr.

If anyone could help me get the proper spine, and point weight I should get to get these things to spine correctly I sure would appreciate it.

Sorry for being such a novice.

[Hermon]

Personally I would use 600 spine arrows for that set up.

[Mr. fingers]

600 for for sure. I ran your numbers but I guessed on your,side plate thickness and the amount of strands on your string .
I got you using  600 at 28.25 with a 200 gr. Point.
I used the 3 Rivers spine calculator check it out its on there web site just click on learn from the,experts then a box will open then click on spine,calculator  and put in you info.
It's fun to play with different combos.

[Dan A]

Hey guys, thanks a bunch for the help.

I wasn't going to bring that up but it was that same spine calculator as I was using but the guy at their shop insisted no, get the 500 even though that was their own spine calculator.

[Ken Sorg]

I'd of never guessed 600 spine and 200gr point! Dan A, you should just order a test kit and have some fun before shelling out $100+ on arrows you are unsure of. I would have said 500 spine, 28.5" and either 125 or 145 point for your (mine also) draw length and draw weight.

[Mr. fingers]

All I did was entered numbers. I ran the 500s at 28.5 with a 145 head.
Bow 42.2
Arrow 62.1
The 2 no. Should be within 2 of each other.

The 600 at 28.25 with 200 gr.
Bow 42.5
Arrow 42.2

[Dan A]

Thanks guys. I do appreciate everything.

Does anyone know if it matters if you leave the arrow a couple inches longer than you need to to make the spine calc come out right with the point I want to use?

I was hoping to use the same weight field points as the broadheads I would be using.

Thanks!

[COMPOUNDLESS IN CONCRETE]

I ran your bow and your info through the 3 Rivers calculator and with a 31" Axis 500 with the 16 grain insert and 150 grain point weight, the Dynamic spine of your bow is 45.6 and the dynamic spine of that arrow is 45.3 so I'd start there and if they aren't tuned just right you should be able to get it tuned with just point weight adjustments.  

That gives you a 460 grain arrow with 16% FOC.  If those tune properly that would be a great arrow to hunt with.

[Bladepeek]

FWIW, I shoot mid-40# bows (38# - 46#) and can shoot 600 spine out of all of them. I'm shooting the 600 spine full length with standard alum inserts and 175gr points out of most of my bows. By going up or down in point weight, I'm sure you can get the 600 spine arrows to shoot perfectly for you.

If you decide to go the 500 spine route, definitely start full length and plan on shooting fairly heavy points out of that Montana - at least 200 gr.

Shorter draws with longbows and mild r/d longbows, and I am one as well, do not seem to have near as many hurdles to jump with cedar and doug fir arrows as with carbons.  . If I were to make a wood shaft first guess for the above, I would say 27 to 27&1/2" bop 40-45 with 125 grain points, if the release is softer than normal 145 grain points, and if the release is harder than normal 45-50s with 145 grain points. This is what the 3rivers gives for a 27.5" 40 pound spine wood shaft.
42.1

Dynamic Spine

42.3

Dynamic Spine

These two numbers should be nearly equal (within 2#).

Fine tuning can then be done by adjusting the bow's brace height.

If the arrow is slightly weak (lower dynamic spine) for what the bow needs, then lower the brace height.
If the arrow is slightly stiff (higher dynamic spine) for what the bow needs, then raise the brace height.
Calculations below are based on the arrow information entered below

Arrow Total Weight (grains) 474.2

Arrow Specific Weight (GPP) 11.5

Front of Center (FOC) % 11.3

Arrow Speed (ft/sec) 171.9

Arrow Energy (ft-lbs) 31.1

[Mr. fingers]

Originally posted by COMPOUNDLESS IN CONCRETE:
I ran your bow and your info through the 3 Rivers calculator and with a 31" Axis 500 with the 16 grain insert and 150 grain point weight, the Dynamic spine of your bow is 45.6 and the dynamic spine of that arrow is 45.3 so I'd start there and if they aren't tuned just right you should be able to get it tuned with just point weight adjustments.  

That gives you a 460 grain arrow with 16% FOC.  If those tune properly that would be a great arrow to hunt with.

That would work too. But that's 5 in.of extra arrow. But you would not have to buy new ones  

[Dan A]

Hey guys, again thanks!

Sorry I was out of pocket for a couple days but after nearly 30 hours of labor we got grandbaby #5 here this morning about 8:30 am.

In my previous post I didn't want to be so obvious about things since 3Rivers in my limited opinion has been an awesome company to business with but it was because of them I ended making this post.

I was using their spine calculator like many of you did. The tech I talked to at 3Rivers said go with a 500 spine, cut at 28" with 125 gr. point for the setup I listed.

When I did that in the spine calculator on their web site it was basically saying this would be way off in spine. I called back and talked to the same very helpful gentleman who said they need to fix the spine calculator and that his original recommendation is what was needed.

So that is why I posted what I did post, looking for confirmation from others on what I should do.

What he told me just doesn't seem to spine right but then again I am a novice at all this and the tech would have lots of experience.

Again, thanks everyone!

[Mr. fingers]

I just sent a pm to Johnathan at 3R. Hopefully he can. Chime in shed a little light on the subject.

[Dan A]

Thanks Mr. Fingers, I look forward to hearing what he says!

[3R Shooter]

Dan A,

I'll talk to the guys to see who you spoke with, but unless they missed the shorter draw length (or if you have brass inserts), I'm not sure why they would recommend that set up.

Now, the spine calculator is a starting point, so don't take it as an absolute, but I would agree with the 600 spine that others are recommending.

Now you can get your 500 spine you have to work, but it will be some heavy point weight. Could buy some brass inserts to help with the weight so you can use standard weight points/broadheads though. The old Axis Traditional have brass inserts, so if you have older models, I would check to see if they are brass already.

[Cavscout9753]

Congrats on the new little one! Sounds like you're in good hands here with 3R. On that note, I use and love the 3R calculator. Its very simple to use, just make sure you enter the data in exactly correctly. It is of course a starting point and not definitive, but has always proved very well for me.

[Dan A]

Thanks 3R but its not really necessary. The gentleman was very cordial and trying to help me the best he could. Me being a novice it could have easily been me misinterpreting how to ask something correctly.

All is good anyways! Been able to confirm the 600 spine and can use the 3R spine calculator to get me to a good starting point.

I've had nothing but great things to say about 3R as they really are the most polite and helpful folks. I feel bad when I call because I am pretty ignorant and ask a lot of questions trying to understand things and staff has never been anything but super nice and they never make me feel like I am asking dumb questions or like they get put out with me with all the questions.

Thanks Cavscout, and yes it is pretty handy. I like being able to play around with the components on there and see how it effects things. Cool tool to use.