Is spine comparable across brands?

[Yard Candy]

I thought for sure this would have been asked but I'm not finding any results here or on Google... I guess I might not be wording what I'm trying to ask correctly.

If I'm using 400 spined carbon arrows from brand A and I want to try out some new carbon arrows from brand B, can I order a pack that are 400 spine from brand B or should I still start with a test kit even though the spines are the same?

Here's full context. The Huntingdoor 400 spine carbon arrows I've been using to 3D target shoot are cheap (I assume) from Amazon. They aren't very durable and don't spin true, but I learned using them. I bareshaft tuned them (cut some length, added some tip weight) to get them flying perfect. I want to upgrade before hunting season. I'd like to try out the Easton Axis FMJs. The FMJs are a smaller diameter, heavier, and both carbon and aluminum. Knowing that the Huntingdoor 400 spine arrows work well with my bow am I good to order a pack of the FMJs in 400 spine, or is it still best to get a test pack with various spines?

I used the 3Rivers spine calculator to compare the dynamic spine of both my Huntingdoor carbons and the FMJs, both spined at 400, and the dynamic spine was basically the same. So I would assume I would be ok.

Just wanted to check in.

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[Rob5589]

I would think that the same spine will get you close. Then just adjust as usual; shortening, tip weight.

 

[wapitibob]

Spine is the result of a standardized test.

 

[Mighty Mouse]

The standardized ASTM test method for determining (static) spine is to hang a 1.94 lb weight from the center of a 28" span of shaft and measure the deflection. A shaft's advertised spine rating is that amount of deflection measured in inches multiplied by 1000 then (typically) rounded off to the nearest increment of 50 or 100 (e.g., 400 spine = .400" measured deflection). So in theory a Brand A 400 shaft would be identical to a Brand B 400 shaft in terms of spine. There might be slight differences in how two different 400 spine shafts behave dynamically due to different spreads between measured deflection and advertised spine and due to differences in the amount of radial spine variation. But generally speaking, different shafts of the same spine should perform very similarly at the same length and front/rear weight distribution.

 

[GLB]

They are close but if you switch brands within the same spine you will still need to go through your tuning process. If your bow likes 400 spine for example then a 400 should work from another manufacturer. They may not wind up the same length when you do the tuning process. Also you will have to consider diameter of one manufacturer 400 spine to anothers‘s 400 spine.

 

[oldgoat]

You did about everything you could, good idea to check dynamic spines too! I'd think you would be ok as long as the lengths are comparable, but don't automatically assume that they will finish out at the exact same length, you will need to tune from full length

 

[Yard Candy]

You did about everything you could, good idea to check dynamic spines too! I'd think you would be ok as long as the lengths are comparable, but don't automatically assume that they will finish out at the exact same length, you will need to tune from full length

That's what I was hoping to hear. I guess worst case scenario you'll see some unused FMJs in the classifieds lol.

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[Yard Candy]

The standardized ASTM test method for determining (static) spine is to hang a 1.94 lb weight from the center of a 28" span of shaft and measure the deflection. A shaft's advertised spine rating is that amount of deflection measured in inches multiplied by 1000 then (typically) rounded off to the nearest increment of 50 or 100 (e.g., 400 spine = .400" measured deflection). So in theory a Brand A 400 shaft would be identical to a Brand B 400 shaft in terms of spine. There might be slight differences in how two different 400 spine shafts behave dynamically due to different spreads between measured deflection and advertised spine and due to differences in the amount of radial spine variation. But generally speaking, different shafts of the same spine should perform very similarly at the same length and front/rear weight distribution.

I knew spine was determined by hanging a weight, so any arrow with the same spine would have similar characteristics in that sense. I just wasn't sure if there were any other big red flags that would prevent two arrows with the same spine from being similar enough to avoid getting a test kit.

I appreciate your response!

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[Yard Candy]

Lots of great responses everyone, thank you.

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[aerophysicist]

The standardized ASTM test method for determining (static) spine is to hang a 1.94 lb weight from the center of a 28" span of shaft and measure the deflection. A shaft's advertised spine rating is that amount of deflection measured in inches multiplied by 1000 then (typically) rounded off to the nearest increment of 50 or 100 (e.g., 400 spine = .400" measured deflection). So in theory a Brand A 400 shaft would be identical to a Brand B 400 shaft in terms of spine. There might be slight differences in how two different 400 spine shafts behave dynamically due to different spreads between measured deflection and advertised spine and due to differences in the amount of radial spine variation. But generally speaking, different shafts of the same spine should perform very similarly at the same length and front/rear weight distribution.

An interesting question that just popped into my mind (especially since the post was just talking about carbon arrows vs. FMJs) would be how spine in different arrows changes with temperature.


Now all of the numbers above are VERY small...but it's easy to see that aluminum will expand and contract a lot more than pure carbon with temperature.

I wonder what would happen if you took a pure carbon arrow and did the spine test in a freezer vs a FMJ arrow.