Shooting spines that should be too light?

[Modad2010]

I got my new 54"Toelke Pika (40# @ my draw of 26.5") a week before Christmas. I had purchase a dozen Beman Centershot 600's as recommended by Dan. Dan had recommended cutting the to 28" and using 75gr inserts and 150gr points. I  fletched up 3, installed 75gr. inserts using Bohning cool flex on the fletched shafts and 3 more shafts (all uncut) and as soon as the bow arrived began shooting with 175gr points. I wasn't trying to tune right away, just getting the string stretched in and getting acquainted with the bow. The arrow flight with this sett-up was great and the bare shafts impacted right with the fletched shafts. I then went to an indoor range and got the same results. Everything I checked said that these shafts should be way too weak, but the grouping and arrow flight didn't lie. I have actually shot them with 125gr., 145gr. and the 175gr. points and gotten good arrow flight. The 125's showed a very slight sign of being stiff, but bare shaft and fletched shafts still grouped well. The 145's and 175's both shot great. I am just wondering is anyone else shooting shafts that defy "what's supposed to be?" I love the bow by the way!

[Orion]

A .600 carbon is about a 51-52# spine.  Given your 26 1/2-inch draw, why would you think that would be weak? In fact, the extra point weight was needed to soften them to accommodate the 40#@26 1/2. Don't know what charts you're using, but IMO they're off.

[Modad2010]

When I plugged all of the numbers into the spine calculator on the 3 River's site it showed the full length arrow with that much weight up front to be under spined. It actually showed showed that trimming to 28" as Dan suggested would be dead on.

 

[Friend]

Calcs showed that your 145 gn w/75 gn insert to be very close

[GCook]

With the calculators the correct shaft, strand count of string, strike plate thickness, center cut and form differential all make a difference on outcome.  You have to play with that number at the bottom to know what I a custom number for you.  As your form and execution improves that number can change.  Thw calculator can get you close.  I always buy full length and work with point/insert weights until I get it right.  Good bowyers and guys like that can put youdang close as well.

Sent from my SM-G892A using Tapatalk

[David Mitchell]

A .600 carbon is about a 51-52# spine.  Given your 26 1/2-inch draw, why would you think that would be weak? In fact, the extra point weight was needed to soften them to accommodate the 40#@26 1/2. Don't know what charts you're using, but IMO they're off.

I totally agree with Orion. And that 52# spine is assuming a standard 28" arrow. My own experience with 600s at 40#@30" and 175 grain points tells me they are not too weak with your set up. The main thing is not what some calculator tells you but what actually works for you.  Calculators cannot figure in your personal shooting factors.

[Orion]

Your spine calculator said a full length arrow would be too weak, but that's not the arrow you're shooting.  Upon good advice, you shortened it substantially, increasing the dynamic spine. Not trying to be a smart axx, but the issue here seems to be a lack of understanding of arrow tuning and/or misinterpretation of what the results mean rather than an inaccurate calculator reading. 

"It actually showed showed that trimming to 28" as Dan suggested would be dead on." In other words, the calculator was right on. 

[Modad2010]

I am shooting a full length centershot 600. I don't know what I am missing with the calculator. The bow was built to #40 @ 26.5 (my draw length), cut to center with a thin strike plate, with an 8 strand FF string. The shafts are Beman centershot 600 - full length (30.5"), 145gr point, 75gr insert, shafts are not footed, nock weight 10gr, no wraps, and 3 - 4" feathers. When I put these numbers into the calculator it shows the dynamic spine for the bow being 46.5 and that of the arrow being 31. What am I doing wrong with the calculator?

I'm not going to change anything with the set-up because I'm getting great arrow flight, but I'd like to possibly use the calculator in the future for help with another bow. Thanks for all of the responses.

[the rifleman]

My Whip is 39# at my draw.  It tunes perfect w a full length 600 beman mfx and 145 grain tip.  Sounds like you are close to what i have.  My 56" pika is 34# at my draw length and likes cx predator iis in 800 full length w 40 gr insert and 125 point.
Charts are usually just a starting point and too complicated for me.  I bareshaft.

[Lakerat007]

Oh man, this takes me back! I no exactly what u r talkin bout. My first bow was used and came with a quiver full of arrows tuned by a guy with a very close d/L. Life was good, then I lost of broke all my aluminums. Started researching sites and such and they had me convinced I was less than "ethical" not shooting high foc and single bevel heads. So to the Carbon I went, except unlike u I didn't play with em. Played with the calculator and had the good folks at 3 rivers chop em off. I was all over the map with a bareshaft. Couldn't figure it out to save my life times like this there's only one fix. The biggest bannanas u can get your hands on, if they made a 10" feather I would have shot it  Eventually figured it out and now buy a shaft one size to stiff, leave it full length and start adding weight. Just the easiest FOR ME. Also went back to my 2017's and life is sweet. Who cares about the why it works for ya, all that matters is it works. Let em fly brotha!

[Coach Jones]

I shot my Toelke Chinook 41 lbs at my 26.5 draw length with a CE Heritage 90 cut 29 inches and 175 grain points and standard insert.   My Kota Kill-um at the same weight likes a 45/50 cedar 5/16 cut 28 inches to the back of a 125 grain point.

[Bldtrailer]

Please remember the calculators are only a ballpark /starting point, first you have to have some good form, then start tuning (bare  shaft http://acsbows.com/bare-shaft-plan.html)  I shoot gt trads 600 from 42@27-up to 55@27 and just adjust the weight forward ,footings

and length.   The above is my DD 51@27w 28 3/8 gt 600 trad 2inch 2117 footings 50grn insert 175 tips bare shaft robinhooded the fletched at 20yrds

[Tajue17]

I guess they help some folks but I learned years ago that those arrow charts are almost useless and dang do they make everything really expensive.  I  never forget what Paul Brunner told me when he worked at screaming eagle and I ordered my first set of custom arrows and I was kinda disagreeing with him about his recommendation on what spine I needed because of some arrow chart ,,,, go by what the arrow is telling you and nothing else or keep your wallet handy is what he said.

unless you have something wrong with your form a bare shaft will tell you how to make pretty much any arrow fly like a laser.

[Orion]

Let me see if I have this straight.  You're drawing 40#@26 1/2 and, according to the calculator, the arrows you're shooting are full length and have a dynamic spine of 46#@26 1/2 inches. (You had indicated initially that you had shortened them.) Regardless, you have an almost a perfect match.  You're not doing anything wrong, nor is the calculator yielding faulty information. 

Most bows will shoot a range of spines (at least 5-15# overspining is quite common). You're right in the wheelhouse.  And the arrows are flying well for you.  There's really no issue here. To expect the calculator to come up with an exact match is unrealistic.  The one thing it can't accommodate/interperolate is your release. It gave you an arrow that's almost a perfect match "on paper." Any other minor discrepancies are due to shooter characteristics.

[Overspined]

Bows cut more to center will shoot more range of spines, and carbons are notoriously stiffer than labeled. I have a spine tester and check everything before I dive in. Orion gives good advice.. I’ve been shooting full length Carbon Trad by victory and in my opinion they are about perfect for trad bows. What I mean is they come already with 80 gr insert, don’t seem to have a stiff or weak side, straight, tight weight groupings, look like wood, and spine right where they should for trad bows.  I have found countless carbons with spines off the charts and it can get frustrating.

[BigJim]

Generally, I wouldn't recommend cutting 600's for a 40lb bow and that more than likely most at 40lbs would do better with a 700 spine if they are going to cut.
I don't believe in spine calculators because there are too many variables that they can't account for.

Guys bend over backwards to make spines work that just aren't designed to work for their set up... but if it works for you, that is really all that matters. Good arrow flight is often an allusion to the shooter. Someone standing beside you can get a much better idea of what is really happening.

I tune close and continue to practice with a set up and make slight tweaks until I'm happy.
Shoot broadheads with your set up. If the field point and the broadhead fly to where you look and do it with decent flight, you can't ask for much more.
BigJim

[Modad2010]

Thanks for all the replies. I'm sorry if I wasn't clear about my setup. I am able to get the full length 600's to bare shaft with my fletched arrows using the 75gr inserts and 145gr or 175gr points. My broad heads also group with my FP's. The 175's show a bit weak, but I have been able to tweak that out with a slight BH adjustment. I do like that I can change the broad head weight in a simple manner and that it allows me to try some different heads easily. I guess for any future bows I'll forget about the calculator and just start out with a bunch of shafts, inserts and points and go from there. Thanks again!

Doug

[pavan]

I have seen about an even three way split with the spine calculators, from too light, to dead on, to too stiff.  With some bows a slight change in brace height can make a substantial change in the spine requirements.

[Alexander Traditional]

I have to agree with Big Jim. He's  the one that got me headed on the right path as far as spine goes. I tell you what, as far as spine goes,and if it's centershot I really can guess the shaft and tip weight up or down if not't right on it. I have bought so many shafts from people that are over spined on the classified.

[Modad2010]

I was shooting today and took three of the fletched arrows with 145gr points and three fletched arrows with 175gr points - both with 75gr inserts just to check differences. Both had good flight, but the 145's group an inch to an inch and a half to the left. The 175's grouped dead on and seemed very forgiving of any form flaws or poor releases. This setup is gonna have a total weight of around 491gr and not a speedster, but will be a great, quiet rig for whietails.