Arrow weight tolerance

[James Park]

Does arrow weight variation matter - yes, definitely!!
To calculate how much it matters:
The first thing you need to do is to calculate the average group size for the archer. This is possible by modelling the group as a Normal Distribution. It is then possible to calculate the Standard Deviation for the group. The average group size gets smaller as the archer gets better, and it gets larger as the archer goes to longer distances. So, for example, it is possible to calculate the Standard Deviation of the archer's group at a particular distance.
For example, my average FITA seems to be about 1350, and on a good day I might anticipate perhaps 1370. At 90M and a score of 1370, that gives me a Standard Deviation for my typical group of 71 mm. That means that 68% of my arrows should land within about a 142 mm circle, and the rest outside that. For a 1350 FITA that would be a 162 mm circle, or for a 1300 FITA a 210 mm circle.
What I need to do then is to compare the enlargement of my group size due to arrow weight variation with the Standard Deviation I get from my normal shooting ability. For the weight variation not to matter much, the group enlargement due to that needs to be significantly smaller than the Standard Deviation - say 1/3 of it. So, for my 1370, I need the height change due to arrow weight variation to be less than about 71/3 mm = about 24 mm. For my 1350 it would need to be less than about 27 mm.
The height change due to the arrow weight variation is calculated by using the same launch angle for the arrow for the given distance, but an arrow velocity amended to suit the new arrow weight. Then by looking at the height of the arrow at the distance of the target, we can get the error on the target due to the weight error. By changing the weight error until the height error is less than our 1/3 of the Standard Deviation we can then get the required accuracy we need to achieve for our arrow weight.
These calculations are exactly what is done in Accurate Sights. Fortunately, you don't have to worry about the maths, but just enter the distance and your typical range score for that distance - Accurate Sights does the rest (and your PC will be doing quite a lot of work in doing the calculations).

[James Park]

If you do this calculation for Clint's 90M World Record (a particularly impressive 347), you will find that he very definitely needed well matched arrows - by my calculation, plus or minus 0.5 grains variation would have affected his score.

For my arrows and arrow velocity:
For a FITA of greater than 1400, plus or minus 0.5 grain arrow weight variation would be too much.
For a FITA of greater than 1275, plus or minus 1 grain arrow weight variation would be too much.
For a FITA of greater than 1200, plus or minus 1.5 grains arrow weight variation would be too much.
Hence, considering my potential best FITA, I need to be guided by these limits, and plus or minus 1 grain would definitely be too great. So: I aim to get them better than plus or minus 0.5 grains (and I think most reasonably competent archers should try to do this as well).

[Marcus]

While there is no arguement from me at all on this one. I believe that ALL archers will benifit greatly from matching arrows. Afterall it you are a grain out you are losing a point each time you shoot that arrow. Could cost you 3 poiunts per end. That means your 282 at 90m becomes a 300. So while your group deviation may already be large, poorly matched arrows will make it larger.

[Zoe]

Jim, this might sound a bit silly andprobably wont make sense, but when you're working out what weight variance is significant for a person of a given standard, what assumptions do you make about the variance of the arrows they're shooting to attain that standard. That is, how do you factor in the possibility that a 1200 shooter may be shooting with a weight variance of 10 grains? If he shot with a .1 grain variance, would this make a significant difference to his score and hence the tolerance range he should be aiming for? (probably not in the majority of cases I guess, considering you use use .5 increments as opposed to a sliding scale)
I assume you assume no variation, in which case wouldn't it just be easier for all archers to weight match to within .1gr considering how easy it is? (basically saying exactly what Marcus said), the point being that while it is interesting to see what is a "significant" variation for a given standard, that given standard is dependant on a variable you can't know? (except if you're Harry Seldon - skilled in the arts of psychohistory of course)In any case, I assume the maths is quite complex :(

My brain hurts, I'm going to bed :cry:

[Marcus]

I believe that the assumption is this.
For a given score there is a standard deviation in group size. If the weight difference is high enough to cause the arrow to fall outside this deviation then it is considered to be too much variation for that skill level.
So if I group at 200mm at 90m and my arrow is different enough that it drops 150mm from the centre of the group then it is doing me a disservice (as my lower arrow would be 100mm from the centre).

Statistically this correct, practically it could be misleading as the arrow would drop 150mm from where I shot it, not from the group.

[Zoe]

I see, apologies (always read the full thread before you post :) )

[James Park]

Zoe,
You are correct. If you are shooting 1300, but with arrows greater than plus or minus 1 grain variation, the weight differences will have already hurt your score and you probably should have scored more.

As both Zoe and Marcus have noted, it is quite easy to get your arrows matched, so the approach I would take is: if you score over 1200, or think you should be, then take the time to match your arrows.

The alternative of course is: just make them all up, number them, go to your longest distance on a calm day and shoot 10 ends or so. For each end, plot where the arrows hit. If an arrow is obviously always going low compared to your average arrow (for example), it is probably a bit heavy. However, it is easier to weigh them first!

I guess this points to the value of clubs owning a grain scale.

[Juggs]

so for an a new commer like me shooting 1200 matching arrows will give me how many more points??

how much are we talking for a grain scale to be able to do this semi accuratly

[2Dogs]

Want a laugh.............I was told by a Source that David Barnes grabs his set of X10's, slaps them all together and shoots them.

No weighing no nothing :lol: :lol:

And he shoots a 1366......1360 recurve.

Now X10's have tight tolerances but still you might get a dud.

So maybe when he figures it out ................anyone for a 1380 :wink:

[Zoe]

I agree that any reasonably large club should consider getting a grain scale. Stevej, as I understand it, you can get an accurate enough scale for around the $100-$150 from a gun shop. They'll be the counter-weight type, but that's cool, doesn't really matter whether it's calibrated within an inch (or grain) of its life, as it's comparisons between what you place on the scale that is crucial. How much better is it that 50 members pay $2.50 for a communal scale (that you use very infrequently), than all 50 members paying $125 for their own scale (that they use very infrequently). [As for how many points correct weight'll give you it should be easily quantified in the Accurate Sights program]

btw Jim, I was not really right, as I was arguing from the wrong premise. For some reason I thought that what was being said was along the lines of: "If you are a 1200 standard shooter then your weight tolerance should be X amount, or it will be costing you points" - noone was saying this of course :roll: (rather "if you shoot a 1200 and your arrows happen to have a variance of more than X, then this variance has contributed to your points dropped). It's just that you and Marcus are kind :D , so I'll say it:
:iamwithstupid:

:D :D :D

Paul, Mike mentioned something about this the other day. I agree, be afraid world...be very afraid :o :o :o

[mike]

It must be said that Jim has scared all us "competent" shooters into action on the arrow weight issue!!

I was really dissapointed the other day when I realised that all my arrows were within 0.5 of a grain bar 1, which I promptly fixed. I was, I admit, hoping for some miracle cure for my recent shooting,but, alas, I was too carefull when I mademy curent set and so, yet again, I am faced with "form issues"!!!!

:roll:

"back to the old drawing board".......

[robbo]

I can see it now, hundreds of archers every where franticaly looking for powder scales, hoping for a significant weight difference in their sets of arrows.

The bigger the difference the better, fix that and maybe sneak some easy points. :lol:

[robbo]

I just weighed mine, + or - 0.9 grns.

Mmmm could be better.

[Tim Cuddihy]

when adjusting arrow weight what is the best way to do it? at the moment im matching heaviest point to lightest shaft. that seems to work within 1 grain but i want to get closer. should i put extra glue behind the points or pin nocks?

[James Park]

I put the heaviest points with the lightest shafts. Then I make a fine adjustment by lightly filing the points of the heaviest arrows.

[GrahamT]

I take a slightly different approach - rather than filing, I use a very fine electronics solder. This can be cut to length and put with the insert/point/shaft combination on the scales. With a soldering iron it can then be melted into the shaft of the insert ( ACE). This way the arrows are brought UP to the heaviest and can be very finely matched. For subsequent changes, simply apply heat and the solder can be removed.
From experience I have has very little trouble with this method.

[Eberbachl]

This is a very interesting topic.

I recently made up a set of lightspeeds specifically for 3D.

After matching the lightest arrow to the heaviest point, all arrows except for one were within 0.7 of a grain. To the rogue arrow I added some hot melt glue into the point to bring that arrow into line with the others.

I think these tolerances are probably fine for the shorter distances of 3D, but for FITA I would most certainly follow Jim's advice and match the entire set to well under 0.5gn variation.

I like your method GrahamT - solder sounds good! Very similar to using hotmelt. They can both be carefully weighed before adding to the points, and can be removed with some heat.

Jim's method of filing is also good, and would certainly allow for very fine adjustments.

An interesting question however, is how much weight could be added or removed from an arrow at the point before the discrepancy in Forward of Centre becomes an issue?

Cheers,

Luke.

:angel: :bday: :angel:

[robbo]

I tried the solder, but couldn't get it to stick. That was with resin cored solder.

Went back to filing.

[Eberbachl]

Most likely you weren't getting enough heat into the joint Robbo.

What were you holding the point with? A metal object such as pliers?

If so, the metal object would act as a heatsink, drawing heat away from the point and not allow it to get sufficiently hot for the solder to bond.

Try drilling a hole slightly larger than the point into a scrap timber block, and sitting the point in the hole to hold it upright. The timber is a poor conductor, and will therefore allow the point to get hot enough for the solder to stick.

For the solder to bond, the point will also need to be clean, and free from grease and residue, and you'll need to use a sufficiently powerful soldering iron. Probably not less than 50W is OK - the higher the better. With a small 20W soldering iron you'll need to heat the point for an awfully long time before it will work.

Anyway, my preferred method is as I said - hot glue. The kind supplied by Easton for use with some of their points. I cut small bits of glue off the stick, and weigh it until I have the required amount, then drop them all into the point itself. Heat the point with a small blowtorch, and the glue will melt inside.

Cheers,

Luke.

:angel: :bday: :angel:

[Ozzy]

Some of these weight adjustment methods seem awfully messy :-?

A few here are using "Blue Tac" in the point/Insert :wink:
I think Ron ("Archery Park") came up with this one.
Must be that lateral thinking lawyer's mind.
:P
Seems ideal to me :wink:

[Eberbachl]

Nah, not messy at all Ozzy :wink:

Just drop bits of hot melt into back of point, then heat with blowtorch. Simple :D

But BluTak sounds like it would work OK.

[DrRalph]

Another thing to watch is wear on the shafts, especially if you have to shoot at strammit. I have some Triples that were shot heavily for 6 months and they lost about 3 grains each, but not uniformly.

If you have a lot of arrows, cycle through them regularly to keep wear even, and check your weights periodicly.

[Marcus]

Yes I found the same, and is a reason why new shafts group so well, but older shafts less well.