Dynamic Spine Calculator

[SeaBear]

Does anyone use the 3Rivers Dynamic Spine Calculator? Once I figured it out and played around with some numbers, it turned out to be dead on the money. I kept my arrows long until I established my form, anchor and release. The calculator showed 28" arrows would be the sweet spot and it was right. They fly awesome. It seems whenever I bring up the calculator in a post people tend to turn their nose up at it. I understand you won't know what works until you actually shoot it but seems to me if you know what youre doing with the calculator it can get you really close if not right on the money.

[PrimitivePete]

Honestly I believe the one factor the calculator can't really answer to, is your form. I believe you can get close with the charts but just like you need to factor that every bow is different, how you shoot also has a great impact that can change the equation. I find it to be hit or miss for me. I have owned bows that preferred heavier arrows, the chart tells my I'm off but the bow tells me a different story. Makes it fun as far as I can see.

[M60gunner]

I use the calculator to get into the “ballpark “ . Only once, and with wood shafts, have it been dead on. But once I have a start I use the method I learned from Ken Beck at Black Widow to refine tuning. I have also been able to “manipulate “ the calculator to accommodate some off the wall arrow/bow combinations. But from what I have seen on social media they may not be so off the wall.

[goose_]

It definitely gets close. For my best Kodiak magnum the preset values for center shot were incorrect. This caused a discrepancy in what I was seeing in the yard and what the calculator was saying. Broke out the calipers and measured the bow, adjusted the values accordingly, and it all made sense.

[WVbowhunter]

Often times it will get you close enough, not perfect but better than any spine chart I've seen.

[Bill from NJ]

The 3R Spine Calculator has worked for me numerous times.
Actually helped me to cut my arrows to the perfect length for me.

[Vroomvroom]

I tried writing a message but I'm on a ship, and the internet is nearly non existant.  coincidentally, I just tried this 5 minutes before reading this forum discussion.   
I"m way off on this chart, but my arrows seem to fly good. I've slow motioned them.   The way I understand, the numbers should be as close as possible?  I'm way off, I think I'm 26 on the bow, and 62 on the arrow!!   
My bow is a martin savannah, I said 1.125 for the strike plate, but not sure.   16 strand fast flight, but again, not sure.    I draw about 27" .   The bow is 55lbs at 28".   

The arrows I been using are 400 spined gt traditional carbons.  I'm thinking I cut them at 30.5".   I have 50 grain inserts and 125 tips, with 5" sheild cuts.  12 grain nocks.      I do know its off a little as these weight in at 520 grains, but on the calculator its 480.    The arrows seem to fly good.   I can't get on the internet 99% of the time currently and I'm away from home for 2 more weeks.  But I do have a few videos of the arrow flight.   When I bought the bow, they supplied 400 spined, traditional only 3 rivers arrows.  Their shorter, but can't say actually.  I'm thinking 29".   125 grain tips, 15 grain inserts, and regular nocks.

[Vroomvroom]

so the 3rivers traditional only 400's are a touch shorter but the same spine with lighter tip weight in total with the 15 grain inserts.   I'm not sure how they fly in general as I haven't shot them in a few years.   I may strip the feathers off of one to see how it flys as I've never checked.   And do the same with the ones I just made up after my form gets better.   But thats the arrows I have.

Supplied: 400 spined traditional only carbons 29" with 15 grain inserts, 125 grain tips, 5" sheild with wraps and 12 grain nocks.
     
               400 spined gt traditional carbons 30.5" with 50 grain inserts, 125 grain tips, 5" shield with wraps and 12 grain nocks...that I bare shafted to 15 yards and cut/fletched myself.

[black velvet]

It gets me close. But I believe it can use some updating.

[tzolk]

Here is what works for me by bare shaft planing arrows per A&H archery and also the Ken Beck video on YouTube. The bare shaft arrows shot from near 30 yards group near the fletched and do not plane too far either way. Sometimes the nocks are a little left or right but according to A&H, that doesn’t matter. It’s where they group in relation to the fletched that matters. As you can see the numbers from the online calculation aren’t even close. Probably if I added a form factor, that might help with other arrow brands. IDK.

[Vroomvroom]

Interesting.  With me, I’m nearly double in numerical difference between arrow and bow.  If this internet keeps working I may order tips in hopes I receive them before I get home in two weeks.  Various weights just to compare.  But I do know when I was cutting my bare shafts I had one full length, it went nock left.  I had one shorter, that flew Nick right badly.   And I had one in the middle of the two that flew straight.     It was really cold etc.  no room at gfs place to shoot.  Maybe this time home I’ll strip feathers off the ones I built to try again.  Seems like everything points to me using a 500 spine.  But I do find the arrows go where I’m aiming 40 yards away.  I sometimes see a movement, but upon inspecting video of the shot, the arrow flexes on take off and within 5 yards starts spiraling and general looks like it’s flying straight.   I haven’t shot in years. But I can hit a 18” block target at 40 yards fairly consistent.   So it seems ok.     Can you post videos here?

[tzolk]

I tried writing a message but I'm on a ship, and the internet is nearly non existant.  coincidentally, I just tried this 5 minutes before reading this forum discussion.   
I"m way off on this chart, but my arrows seem to fly good. I've slow motioned them.   The way I understand, the numbers should be as close as possible?  I'm way off, I think I'm 26 on the bow, and 62 on the arrow!!   
My bow is a martin savannah, I said 1.125 for the strike plate, but not sure.   16 strand fast flight, but again, not sure.    I draw about 27" .   The bow is 55lbs at 28".   

The arrows I been using are 400 spined gt traditional carbons.  I'm thinking I cut them at 30.5".   I have 50 grain inserts and 125 tips, with 5" sheild cuts.  12 grain nocks.      I do know its off a little as these weight in at 520 grains, but on the calculator its 480.    The arrows seem to fly good.   I can't get on the internet 99% of the time currently and I'm away from home for 2 more weeks.  But I do have a few videos of the arrow flight.   When I bought the bow, they supplied 400 spined, traditional only 3 rivers arrows.  Their shorter, but can't say actually.  I'm thinking 29".   125 grain tips, 15 grain inserts, and regular nocks.

I see 500 spine arrows on this set up all day long with arrows cut that short and light weight tips. Don’t know if it was a typo but you said a strike plate of 1.125. That would be over an inch. Should be 0.125.

[Vroomvroom]

tzolk, In my hurry where the internet cuts out here.......I may have typed that in, i'm not sure.  I just did the same calculation.   savannah 55 at 28.   27” draw. 16 strand fast flight. .125 strike plate.    GT trad carbon 400's with 125 tip and 50 gr insert, three 5" feathers with a 12 gr nock, and it’s closer than what I got earlier.  It is showing 50.8 to 62.6   So thats closer, and similar to your differences.    I will strip one arrow off eventually when I get home.  Or at some point the weather gets better.   

for giggles I put in 175 gr tip, otherwise leaving all the rest the same.   The two numbers were near the same, 50 and 51.9.  Might have to try a 175 gr to see how it flies.

[SeaBear]

for giggles I put in 175 gr tip, otherwise leaving all the rest the same.   The two numbers were near the same, 50 and 51.9.  Might have to try a 175 gr to see how it flies.
[/quote]

I'm shooting 175 gr tip, 74 gr insert, 28" GT traditional 500 and they fly like magic for me. I left them longer while I established my form and release and started cutting them shorter to tune. The calculator was dead on the money for me.

[Vroomvroom]

What was your bow and poundage? Draw length ?

[Vroomvroom]

But even with the last arrows I purchased in 400 spine. It seemed every spine chart I looked at for my heavier bow. Martin savannah 55 lbs at 28” drawing 27” or a hair less recommended a 400.  But everyone always figured I should have ordered 500s.   

The roots recurve is only 49# using a b55 string and I’d like to try the gt classic xt with the  ballistic collar. Those are heavier. I’m expecting 500s might be ok there. But the 400s seem ok with the 50 gr insert and 125 gr head. The arrows are maybe longer than most would have them.  But I google gold tip spine chart using recurve and longbow , arrow length, tot as k tip weight.  I always get in the 400 range or on its border with 500.    I wonder if wraps, and those inserts are long, if they stiffen the arrow up s little more than the charts recommend.    The more fact weight the longer those things get