Spine Charts

[YosemiteSam]

I've done fairly well in the past with 3 Rivers' spine calculator.  But I'm getting some funny data & would like some input.  

Bow:
typical Samick Sage - 50# @ 28"
Drawn to about 26.75"  
Bear Hair rest (had a Hoyt flipper rest but recently switched to the Bear Hair)
Fast flight 12-strand.
Beaver ball string silencers.

Arrows:
Gold Tip 340 (7595, right?)
32" (full length),
100 grain inserts
200 grain heads
3 5" feathers
standard nock.

According to the calculator, my bow should require a 56.3# spine and my arrows are deflecting at a 47.3# spine (weak).  Yet my arrows most consistently tail nock right (right handed so a stiff reading).  It's not much.  But it's there.  About 1/4 groups of bareshafts will fly perfectly straight but most tail right and, after about 25-30 yards, veer left on the target.  It was more pronounced when I had 50 grain inserts and less so with 100 grain inserts so the trend is correct -- more weight = straighter flight.  But the calculator seems way off for me.

Is this a form issue?  Or would some of you say that I'm shooting a stiff setup, regardless of what the calculator says?

Big Jim - this was something that you hinted at when I was shooting similar arrows from 45# limbs.  The Hoyt rest appears to have been masking some of the spine issues you mentioned.

[Buckeye1977]

I would say those shafts are too stiff but I'm kinda new to the tuning game. I shoot gold tip 500's out of my 50#@28 longbow and only draw about 26.5. My point weight is about 200 grains and they bare shaft perfect.

[crazynate]

I'd say they are to stiff. Problem with heavy points like that is when we bare shaft we're concentrating more on form and expansion but when we shoot we don't always have the exact form. At least this is what happens to me. So if you short draw even a little or creep forward than your not getting the full power behind your shot and your arrows that bare  shaft well are  not flying well.  When I switched arrows to lighten up my tip weight I get less issues. This is just my observation from hours on hours of tuning and tweaking. Having a flatter flying arrow seems to work better for me.

[rraming]

Try 500 Spine Shafts

[tecum-tha]

I have no idea why you guys are all shooting these long arrows?

I assume your draw length is measured correctly from the deepest part of the grip. Then your AMO draw length is 28.5".
I give you a best length of 30" BOP, that leaves 1.5" to protect your hand from a broadhead.
If you measured your draw length from the front of your bow, here is your culprit.
If you use a 5/16" equivalent shaft, you are still within the wood shaft procedure.
50# Recurve+8# for the fast flight string+10# for the Recurve+ 4#x7 for every 25 grains point weight over 125 grains (300-125=175 175/25=7)+ 5#x3.5 for every inch over 28.5" (32-28.5=3.5) for a 32" arrow= 50+8+10+28+17.5=113.5 Calculation for aluminum/carbon deflection:
(26/X)*1.2115=113.5
Solve for X=(26/78.5)x1.2115=0.277
Carbons react somewhat stiffer, because of less mass per inch in comparison for wood. For this shaft this is not such a big effect.
A .300 shaft should be right and your arrow shows also weak in the calculator.
There can be two things:
1.) Your bow is cut past center and the hair rest make your arrow tip point to the right of the plane of your string. That makes for very unfunny conditions. And the Hoyt rest probably was center shot or had the arrow sticking to the right of the string plane which is the normal condition.

2.) Form issue, but I tend more to 1.)as the calculator worked ok with your other bows.

[YosemiteSam]

Originally posted by tecum-tha:
I have no idea why you guys are all shooting these long arrows?

1.) Your bow is cut past center and the hair rest make your arrow tip point to the right of the plane of your string.

2.) Form issue, but I tend more to 1.)as the calculator worked ok with your other bows.

I shoot the long arrows because I like heavy arrows.  Tiny gaps are more idiot-proof since they are mostly on the target somewhere from 0-25 yards.  I had 400s but they zinged out so fast that my gaps were measured in feet, not inches (even 3-under).  The 340s at full-length are 605 grains and never rise more than 10" from 0-20 yards.  I've not yet set my gaps for the same arrow at 655 grains but so far, they're even tighter than that and my PO distance is about 24 instead of 26 yards.  Keeping my shots within that 0-20 range = small, reliable gaps for hunting.

1. The riser is cut to 3/16ths past center.  The Bear Hair rest is about 1/8" so that nets 1/16th past center.  With a shaft diameter of 5/16, the arrow is definitely outside of center at rest.  A quick visual confirms this -- the arrow lies left of center.  But the Bear Hair rest is a harder material than the Hoyt rest so that may be an additional variable.

2. I need to video myself so I can see if I'm plucking.  I also nick my armguard fairly often so this is probably throwing things off, too.  Can't seem to avoid it, no matter how much I turn my bow arm inward (just slaps higher up my forearm).

[Echo62]

75/95 is too stiff. 500 spine 35/55 should work. That said, you might get 400 55/75 to work full length with 300 grains up front. I shoot a 500 spine, 265 up front, 31" length. My bow is 47# at my draw length and that set up works for me.

[tecum-tha]

You nick your armguard fairly often?
I think it is then your inconsistent grip when it comes to rotation around the longitudinal axis of the riser.
Put an indexer on the grip and see if that helps.

I guessed you gapped. The only reason to shoot an arrow which is too long,lol. To each their own.
Arrow mass is no reason, you can fill your arrow with cord and get a favorable mass and FOC distribution, too. I think your arrow is probably pretty slow out of this bow...

[M60gunner]

Nothing personal or demeaning but I would start over with a different bow. A metal riser bow like a Hoyt Excel. Your gap system with the heavy arrows will work better. The riser is cut well past center to allow you the adjustments you need.

I have with my Excel riser and 55# limbs shot 75-95's as well as 2419 aluminum arrows. Of course the spine calculator did not always agree but by maneuvering shaft length, point weight I could get close. At 20 yards those heavy arrows really hit well. It was after that I was not happy with the trajectory.

Agian, my personal thoughts based on my experience. Your thoughts and experience may vary. Then agian you may not like metal risers.

[YosemiteSam]

Originally posted by Echo62:
75/95 is too stiff. 500 spine 35/55 should work. That said, you might get 400 55/75 to work full length with 300 grains up front. I shoot a 500 spine, 265 up front, 31" length. My bow is 47# at my draw length and that set up works for me.

So, I'm guessing the spine chart is off for you as well?

[YosemiteSam]

Originally posted by tecum-tha:
You nick your armguard fairly often?
I think it is then your inconsistent grip when it comes to rotation around the longitudinal axis of the riser.
Put an indexer on the grip and see if that helps.

I guessed you gapped. The only reason to shoot an arrow which is too long,lol. To each their own.
Arrow mass is no reason, you can fill your arrow with cord and get a favorable mass and FOC distribution, too. I think your arrow is probably pretty slow out of this bow...

I think I understand what you're saying on the first part.  Forgive my ignorance -- what is a grip indexer?

Yes, the arrows are quite slow by comparison to most.  I've never chronographed an arrow but, by the same charts that I'm now questioning, I should be coming in between 150-160 fps.  If I was shooting 3D or lobbing arrows from any distance, this would clearly be problemmatic.  But from 0-20, I love those gaps.

[Orion]

Shafts are way too heavy.  Can't believe the spine chart would recommend 340 shafts for about a 47# draw weight.  .500s, which are two spines lower, should work much better.

[YosemiteSam]

Originally posted by M60gunner:
Nothing personal or demeaning but I would start over with a different bow.

...

Then agian you may not like metal risers.

I'm not married to my equipment & wouldn't ever take a criticism of it personal -- heck, I didn't make it.  

Just the same, than you for your thoughts here.  Much appreciated.

[YosemiteSam]

Originally posted by Orion:
Shafts are way too heavy.  Can't believe the spine chart would recommend 340 shafts for about a 47# draw weight.  .500s, which are two spines lower, should work much better.

I wish there were more traditional archers out here.  The guys at the local shop gave me all sorts of skeptical stink eyes when I kept increasing my point weight on my 29" 400s with 45# limbs.  One of the shop owners swore that 125 gr heads with 12 gr inserts would be just fine.  But they're all compound guys & only break out the recurves a few times a year.

It seems that the consensus is that the spine charts aren't always accurate.  I appreciate the sharing of how things have worked out for everybody in real-life.

[Orion]

The spine charts do tend to recommend arrows that are a bit stiff, according to what i've read.  Don't know. Don't use them.  But I've been shooting sticks for so long that I just know what's going to work for my bows.

It is important to factor in the effects of sight window depth, string material, sought after arrow length, weight and point weight, bow weight at the shooter's draw length, etc. Stu's calculator is supposedly pretty good at incorporating these factors, plus an individual shooting form factor, which takes some time to determine based on previous experience, to come up with a spine that will put you in the ballpark.  But for it to be effective/accurate, all of the factors must be known and plugged into the formula.  

Compounds, because they are cut past center, and because they are shot with a release, can be shot with just about any spine over the minimum required for the bow.  The recommendations they were making would work for compounds, but not stickbows.

Keep plugging away and asking questions on here.  It will come around eventually.

[tecum-tha]

A grip indexer is something you put on your grip that make you grip the bow the same all the time.
The indexer is there to prevent that you lock the riser in a torqued position during the shot. Every bow has its sweet spot for that. For instinctive shooters, that is when the bow is quiet and shoots where you look. It is the place position where your release hand induces the least left-right oscillation upon release. It is therefore not always the position where the string would be perfectly aligned, as your left and right movement during release can vary. That especially applies if you hold your bow tight and do not put pre-tension on the string.

Basically, there is a +/-15# personal form factor in the spine calculator as well. In carbon that can make a full spine group.