Spine variances when shafts are cut short.

[Pac8541]

Is there any kind of formula or constant that carbon shafts change in spine as you cut them down?

Same question as it relates to increasing point weight.

Everything I've read and everyone I talk to says spine increases when I go from a 32" shaft to 26 inches. And adding point weight decreases spine. The issue comes up when for my specs, I fall on a line between spines. I get that a 350 shaft, for example, has some range stiffer and weaker and it's desirable to stay within that window. I'd like to stay on the stiffer side of "optimum." But where that line winds up after cutting and loading the front becomes cloudy when I don't know how much of an effect each has.

Is software like archers advantage accurate enough to place all my faith in? I've been as complete as I can entering all the info it requires. But I think it's a relevant question if I'm spending $150 on bare shafts and won't know how they shoot until they're completely assembled.

 

[tipsntails7]

short answer is those programs are close enough. With modern bows and drop away rests i will always go stiffer, i really don't think within reason you can have to stiff a spine anymore.

 

[camping1601]

I've used that program with good results. I go a little on the stiff side myself.

 

[Pac8541]

Appreciate the input. I've ordered a few shafts and gonna see if I can find somewhere local that has a spine tester. I might be taking this too far but for my own education I wanna know.

 

[Hoytgamer]

I agree with the above comments. You can be a little over stiff on the spine but you dont want to be under spined. One thing that helped me when i was getting false center shot reading paper tuning was making sure the cam lean has been tuned out at FULL DRAW. Its done by yoke tuning. Other wise your bow will torque the shot through the paper and youll struggle with wondering if you spine is to weak. Happened to me, and learned through pain and money. Just food for thought. I would just recommend that you find a Pro shop with someone knowledgeable on the subject.

 

[Pac8541]

short answer is those programs are close enough. With modern bows and drop away rests i will always go stiffer, i really don't think within reason you can have to stiff a spine anymore.

Which program would you say is the most accurate? I have both Archers Advantage and OT2 but I'm not opposed to looking at others.

 

[tipsntails7]

Which program would you say is the most accurate? I have both Archers Advantage and OT2 but I'm not opposed to looking at others.

Either of those is what I would use, I don't think anything out there is better.


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[BackcountryMT]

Both will be plenty accurate to get you at a great starting point. I like a really stiff arrow for my setups.


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[Pac8541]

The biggest question mark arises when I get different or vague results out of each program. OT2 is nice because it has a sliding spine scale and actual numerical values for where the pointer is. AA, not so much. Terms like, "slightly weak" or "moderately stiff" are so subjective.

Right now, with identical data points input into both programs I get results that are within 4/10ths of a grain total arrow weight but OT2 says I have a spine of 317 (on a 300 shaft) whereas AA has the slider maxed to the right at "too stiff" for the exact same shaft.

 

[BackcountryMT]

What are the specs on the arrow(length, head weight, any special weights up front)? And your bow specs(draw weight, length, model of bow)?


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[Pac8541]

What are the specs on the arrow(length, head weight, any special weights up front)? And your bow specs(draw weight, length, model of bow)?


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Shaft: Black Eagle Deep Impact 300.
Length: 26" (CtC).
Head weight: 202gr (point plus footed insert).
Fletching: 4X 3" feathers.

Bow: Elite E35.
DW: 71lbs
DL: 27.5"

Both programs have been "calibrated" by inputting personal specs and chronographed arrow speeds.

 

[BackcountryMT]

Shaft: Black Eagle Deep Impact 300.
Length: 26" (CtC).
Head weight: 202gr (point plus footed insert).
Fletching: 4X 3" feathers.

Bow: Elite E35.
DW: 71lbs
DL: 27.5"

Both programs have been "calibrated" by inputting personal specs and chronographed arrow speeds.

For all intents and purposes, you're "way overspined" but just fine. I ran 182 grains on the front of a 26" GT Pro340 through a 74# Impulse 31 at 27.5" with zero issues in tuning or broadhead flight.

 

[theleo91386]

Choosing the spine that will work shouldn't be this difficult. For most there's 3 option and if you are going really heavy or long there's 4. Look at the manufacturers chart and if you're border line between spines, go with the stiffer spine. If your setup is a little out there from what you see for free online, call the manufacturer for free and they can tell you which way to go.

 

[Pac8541]

Choosing the spine that will work shouldn't be this difficult. For most there's 3 option and if you are going really heavy or long there's 4. Look at the manufacturers chart and if you're border line between spines, go with the stiffer spine. If your setup is a little out there from what you see for free online, call the manufacturer for free and they can tell you which way to go.

Totally agree, it shouldn't be this hard. I deal with values like this, measured to the Nth degree, on a daily basis as a profession. Part of that is required by the job itself but more is due to my personality. From what you guys are saying though, I think I've figured it out enough to proceed. I have talked to B.E. directly in addition to Perry at South Shore and Dorge at Firenock. Appreciate the info gents, thank you.