Spine: What should be vs what is.

[justbinfishin]

Heya folks. I haven't posted in years, so I am glad to see you are still here and awesome!

I recently went to set up my Samick Journey with new 50lb limbs for moose and caribou hunting, and I wandered down to a box store to pick up some arrows. I had a few options from the 3rivers spine calculator, and I basically wanted to get arrows that will work with 125gr heads (very little selection in Fairbanks AK, no one even carries zwickies except the one pro shop, and they were out). 

So, I went home with some Easton GameGetter 400's with 3" helical vanes (I have a NAP Flipper rest installed). 3 rivers said these should be far too weak at 32", but just about right at 31.  I stripped the vanes off of one shaft, screwed on a 125gr field point, and let it fly from three yards...... Extreme nock right. I shot two more times to confirm, and it was way off. I then dug around through my assorted broadhead and field point pail and weighed a bunch of points.  I continued working my way up until I found something that went in straight; a 155gr no name cut on contact.

By the numbers, the dynamic spine of these arrows with the broadhead that bare-shafted straight is about 62, while that of my bow is in the mid 70's (I overdraw to 60#, and the limbs while marked 50# actually pull a measured 55# at 28).

I have been told form affects spine, but I really don't see it being over 20%.

And now, my question.  What parts of form can affect spine in a big way?

My only other trad bows have been Martin longbows, and I was fortunate enough then to live near a good shop where I could bare-shaft shoot carbons until I found one that was slightly weak at full length, and I have never had to use this calculator or route before. I will try to figure out the dynamic vs calculated spine for my longbow and arrows when I get around to it.

I'm hoping you guys and gals can enlighten me, and maybe I need to hunt down a coach to work out some freakish lapse in my form.

[DanielB89]

I wont be of much help, but, in my experience, I have always ran a .340 spine arrow for that weight bow.  Some times you can get false readings if you're way out of tune.  My arrows are typically on the stiffer side and I have had several people question my spine selection.  All I can tell you is what has worked for me.  I believe I have a horrible release, which plays a major role in that, imo. 


Good luck, someone should be along here shortly that is much smarter than myself! 

[bigbadjon]

The biggest factor in effecting arrow spine is draw length. I would be surprised if you could not get that shaft to tune if left long and set to center shot. How close to center is your arrow on your flipper rest?

[justbinfishin]

Samick sage/journey risers are cut .1875 past center, and my flipper rest is 0.0625 thick. I draw between 29.25 and 29.5" depending, at a measured 60.5lb

[bigbadjon]

Tape a string dead center of you limb bolts running down your riser. Is your arrow tip to the left of that line? I am assuming you are right handed.

[J. Cook]

In most of these "too stiff" issues, the problem is often that you think you draw farther than you actually do.  If you haven't done this before - have a friend mark your draw on your shaft with a sharpie when you are settled to your anchor point. 

I always needed a weaker shaft combo than what the calculators showed me...that is until I learned I was off on my expected draw length by a full inch.

[LBR]

String (material, how it's made, etc.), nock fit, your release...all can have an effect on your spine requirements.  I agree with J. Cook on the draw length also.

[Orion]

If I understand correctly, you only had to increase the point weight 20 grains from what you wanted to get good arrow flight.  I'd say that's very close.  Go with it.

[justbinfishin]

I will check my nock fit, as I haven't touched them yet.  My draw length has been measured multiple times at archery shops with a DL arrow, most recently being 5 minutes before I purchased these shafts at Sportsman's Warehouse.

"Just roll with it" isn't particularly helpful, because I bought these with the explicit intent of using 125 grain (30 grains lighter) heads that I can buy locally, which I think I said in the post.

I will indeed use them during moose season (this will perfectly match the combined weight of my zwickey eskilites and screw-in adapters), but no one makes a screw-in 160 grain judo point for stump shooting and knocking grouse out of the willows.

I appreciate the ideas folks! I am just trying to wrap my head around what parts of form can have a large impact on spine. I see how plucking the string would move the nock to the left, but I may just be lacking in imagination.

[CoilSpring]

With your hands, bend out a 40-45 gr 22LR projectile from its case. Cut off the crimped lead part with wire cutters, remove your alum insert, add hotmelt to the remaining lead & alum insert, install both in shaft, allow to cool.  Now, you're tuned. Kill a big un 

[Orion]

Even perfect form won't make an arrow fly correctly if it's not matched too the bow.  The spine calculator got you in the ballpark, and you found a head weight that shoots good.  May not be what you want, but that's sometimes how its works.  Broadheads of the weight you need may not be available locally, but the choices are almost unlimited from mail order shops. 

Adaptors also come in a range of weights from 20 to 50 grains in aluminum to 75 to 125 grains in steel.  These, too, are available from mail order vendors so you should be able to work up the correct judo point front end weight you need. 

[Cyclic-Rivers]

I agree, local pro shops usually are not able to carry the selection you need. They or you can usually order what you need. As mentioned previously there are broadheads and adaptors in all weights virtually.

As far as bare shafting and tuning, all I can say is good luck. Some bows are easy and others not so much. I used to live near Ron W. He would always figure out my stubborn ones for me.

[BigJim]

you are putting way too much trust in a spine calculator. Plus, getting measured by having someone mark your arrow will only give you ball park draw length.
Most everyone will draw differently when bearing down on a target than they do while posing for a draw measuremtent.
Most everything you need for trad is avaliable within 3 days .. roughly via usps.
BigJim

[Don Stokes]

When I was in the arrow shaft business I matched up hundreds of people using bare shafts. I found that most people overestimated their draw length, and it seems that every variation in form has some effect. It was not at all unusual to come up with the proper spine for someone, and the next guy, with a similar setup, needed something different. A test set is the best solution.

[justbinfishin]

Thanks for the input guys, I was out three days and got a nice caribou (rifle, so it barely counts).

I stuck some eskilites with 45 grain alum adapters on there, and filling the hollow tip with hot-melt brought the weight up to 157. They fly like darts to 30 yards so I'm happy with these shafts for caribou and maybe moose. I'm gonna stick with it. Perhaps I will find some beater carbons for stump/bunny shooting with my 30lb limbs, but I'm never doing this again without a test set.

As a point of interest, I put a shiny sticker on my shafts at 29.5, and took a video of me shooting. I am hitting the sticker almost every time at anchor. Now I wonder if I'm subconsciously changing it up... But I have a workable combo so it's time to stick some critters.

**Edit. I'm 6'4" with a 76.5" span, so 29.25" is a pretty short draw length for my dimensions already.


Cheers!