Shafts Weight seems out of tolerance

WinBase

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Hi

ive just purchased a set of ACC 3-04 680 arrows from the easton T5 section, which are *supposedly* the best spine for my poundage of 34lb and 29". these are advertised at 7.2 grains per inch.

after building them and comparing them to my old slightly stiffer set of 3L-18 620, (7.5gn per inch) i was really surprised to find that the weight has gone up when im using exactly the same same nocks, fletchings, uni bush and pile, in fact the old pile weighed 82 grain and my new ones 80).

the weight comparisons are 319gn for the 620's and 323gn for my new 680's fully built.

ive weighed each componont accuratly and by my calculation expected a small overall drop of about 10gn or so per arrow (28.875 * 0.3) + 2gn for the pile, instead its risen by 4gn.

while i realise that to be out by about 14gn isnt much, how can this be? any ideas welcome, as it's the 680 shaft thats heavier than the 620, and appears out of the tolerance id expect.

thanks

Bob
 

bimble

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have you calculated the theoretical weight of your old one? In case it's not a case of you new ones being off, but your old ones... especially if they're very old and worn...
 

WinBase

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good thought, and i thought that at first but the calculated weight of the old arrows was pretty much spot on. i calculated at 319.1 and 7 older arrow weighed from 318.5 to 319.6
 

Timid Toad

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14gn overall is a lot. However, what's the spread a cross the whole set? If they are pretty close (say, within 3-4gn tops) I'd not worry too much. If the spread is wider, I'd be looking to chat with my supplier. Where did you get them from?
 

bimble

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curious... and there's no chance they've sent you 100gr points... because short of weighing all the individual components and seeing which one is off I don't know...
 

dvd8n

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If you weighed all of your components and the assembled weight is more than you expect from the sum of the components then you must have missed something.

Arrow wrap? Glue? Labels? Arrow longer than you think?
 

WinBase

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the first thing i thought was 90gn points so i took one out of the new arrow and it weighed 80.5gn. i also weighed each individual component (nock, unibush, fletching). i did find the new 1.75" bohnig x-vanes to be .4 gn heavier than the old ones though which would account for a fraction

to simplify things i weighed both bare shafts nocked & piled

620 was 307.6gn with 82gn pile, 3.2gn unibush, 6.7gn g-nock (i weighed each item)
680 was 309.3gn with 80.5gn pile, 3.2gn unibush, 6.7gn g-nock

the fletchings were 4.0gn each for the old ones, 4.4gn each for the new ones

620's advertised at 7.5gn/in 680's 7.2

thanks for the input
 

Rik

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You may just be hitting the general problem with carbon shafts: the spec can be a bit fuzzy. It's not like alis where the consistency is high. When they talk about "matched sets" of X10s - you get that kind of match with a handful of random shafts pulled from the same size with alis.
So, you may be seeing just a set of ACCs on the heavier end of things. The nominal weight may be "7.2" but in reality, that will be "7.2+-x" and I don't know what "x" is for ACCs.
 

Timid Toad

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I have a "matched" set of C2 X10s and a "matched" set of C4 X10s, and while the spread within the sets is pretty close (3gn max and some of that could be glue inside the second hand shafts) the difference between C2 and C4 is 7gn. It's quite normal, even within the same spine.

So my concern is always what is the difference between the heaviest and lightest arrow in your set. While ACCs are not made to the same tolerances as X10s, and the nibb points are pretty shockingly poor (imo), if they come up fairly close you'll be ok.
 

WinBase

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Hi Rik

The easton website says the weight tolerance on ACC's is +/- 0.5gn (presumably per shaft not per inch lol)

Heres the exact Figures both theoretical and measured for bare shafts nocked and piled. as you can see the 620's come out with a negligible difference to theoretical/actual, but the new 680's i bought are 11.1 gn, which seems rather large in archery terms where the smallest amounts matter, especially as i currently need all the help i can get at 90m to keep the sight mark on the target


QtyGrainsTotal

------------------------
3L-18/620 Shaft 7.5 gpi28.887.50216.56
Nock1.006.706.70
Bushing1.003.003.00
Pile1.0082.0082.00



=======
Theoretical Weight

308.26
Actual Weight

307.60
Difference

-0.66














3-04/680 Shaft 7.2 gpi28.887.20207.90
Nock1.006.706.70
Bushing1.003.003.00
Pile1.0080.5080.50



=======
Theoretical Weight

298.10
Actual Weight

309.20
Difference

11.10




Shaft Only Weight


219.00
Actual Shaft Gpi

7.58
 

WinBase

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I have a "matched" set of C2 X10s and a "matched" set of C4 X10s, and while the spread within the sets is pretty close (3gn max and some of that could be glue inside the second hand shafts) the difference between C2 and C4 is 7gn. It's quite normal, even within the same spine.

So my concern is always what is the difference between the heaviest and lightest arrow in your set. While ACCs are not made to the same tolerances as X10s, and the nibb points are pretty shockingly poor (imo), if they come up fairly close you'll be ok.
i built 9 of my new arrows and the spread across all 9 fully built arrows was 322.6 to 324.2 (1.6gn) which im happy with, but as these arrows are 11gn each over the theoretical value, it seems a lot
 

Timid Toad

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i built 9 of my new arrows and the spread across all 9 fully built arrows was 322.6 to 324.2 (1.6gn) which im happy with, but as these arrows are 11gn each over the theoretical value, it seems a lot
So my guess is that they are within what Easton thinks are reasonable. They are interested in what they spine at, so as long as they are in the 680 area theyll be happy.
Have you shot them yet?
 

WinBase

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No i havent shot them yet, im just about to take back to the shop to get them checked as being the right spine and to see what they think.
 

dvd8n

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So have you weighed a shaft or just calculated it? I'm not clear....

The other possibility is the accuracy of your scales. How confident are you of their accuracy?
 

WinBase

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dvd8n: I both calculated and weighed the arrows as shown in my earlier post, with each new arrow weighing 11gn heavier than what would be expected based on the easton chart.

Ive just had them checked out and talked to the guy at the archery shop and he assures me the spine is ok, & a spead of 1.6gn between each arrow in the set is good, and although he found the same as me that the actual arrow weight is 11gn > the calculated weight, said it was nothing to worry about as the easton tolerence is +/- 0.5gn PER INCH, which makes my actual GPI of 7.58 within the tolerance that easton advertise for these arrows of 7.2gpi, & is due to manufacturing. He said its the spine & weight match across the set that's important (as others have said & what i assumed) with the GPI not to be worried about (which i wasnt sure)

so to summarise i have a set of supposedly lighter arrows that weigh more than expected heavier ones. & although The difference seems a lot to me for such a precision piece of kit as an arrow, i'll have to bow to those that know better than I, & at least have learned something new :)

thanks to all for the input.
 

Timid Toad

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Upsides and downsides:
A heavier arrow may give you poorer sightmarks at distance. But as it's a lighter spine it probably is a skinnier shaft so less air resistance, and that extra mass will give you better groups at the further distance. They'll leave your bow slower, but retain more energy downrange. so less prone to drift.
 

WinBase

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Upsides and downsides:
A heavier arrow may give you poorer sightmarks at distance. But as it's a lighter spine it probably is a skinnier shaft so less air resistance, and that extra mass will give you better groups at the further distance. They'll leave your bow slower, but retain more energy downrange. so less prone to drift.

Thanks TT

ive just shot a couple of dozen at 20yds and first impressions is that they fly beautiful and the bare shafts were grouping instead of the stiffer bare shafts arcing off left and low. im lucky to have a sheltered 20yd range at home so will spend another few hours tuning and give them a go at the longer distances next chance i get.
 

Rik

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dvd8n: I both calculated and weighed the arrows as shown in my earlier post, with each new arrow weighing 11gn heavier than what would be expected based on the easton chart.

Ive just had them checked out and talked to the guy at the archery shop and he assures me the spine is ok, & a spead of 1.6gn between each arrow in the set is good, and although he found the same as me that the actual arrow weight is 11gn > the calculated weight, said it was nothing to worry about as the easton tolerence is +/- 0.5gn PER INCH, which makes my actual GPI of 7.58 within the tolerance that easton advertise for these arrows of 7.2gpi, & is due to manufacturing. He said its the spine & weight match across the set that's important (as others have said & what i assumed) with the GPI not to be worried about (which i wasnt sure)

so to summarise i have a set of supposedly lighter arrows that weigh more than expected heavier ones. & although The difference seems a lot to me for such a precision piece of kit as an arrow, i'll have to bow to those that know better than I, & at least have learned something new :)

thanks to all for the input.
Ah, yes. You see I would assume that tolerance was per inch, because that's the way they quote shaft weight, and talking about a whole shaft weight would not make sense, as each person would be cutting to different lengths.
It's a bugger if you're trying to figure out the theoretical effect of a shaft change on sightmarks, but probably doesn't have a great deal of effect otherwise.
 

backinblack

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Ah, yes. You see I would assume that tolerance was per inch, because that's the way they quote shaft weight, and talking about a whole shaft weight would not make sense, as each person would be cutting to different lengths.
It's a bugger if you're trying to figure out the theoretical effect of a shaft change on sightmarks, but probably doesn't have a great deal of effect otherwise.
That's odd because I would have assumed the opposite: I've typically found a dozen cut shafts to be within a spread of a couple of grains overall which almost certainly wouldn't be the case if it were +/- X grains per inch. That said, I've only gone to the trouble of weighting X10 or ACE shafts so it may not apply to ACCs...
 
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