How much arrow weight variation affects accuracy?

[bryan]

G'day,

I was wondering how much arrow weight variation people find acceptable for accurate shooting? This question comes about after I recently made 20 odd bamboo arrows with fields points. I weighed them all and bunch them in groups 530gr, 570gr, 600gr. All arrows with in 10grs of each group so the biggest variation is 524gr to 609gr. I marked each arrow with its respective group however at the range I can't notice a difference between weights. It seems no matter what weight they are I still seem to use the same point of aim and achieve 5inch groups at 20m( all arrow rights in that same group ). So at what variation does it make a difference?

[littlejohn59]

Heaps!
The longer the distance you shoot at, the greater the arrow will drop away. Obviously at 20 m its marginal as you are much closer to the target. Shoot the same arrows at 25,30 40 and 50 meters distances and observe your results.

[discord]

Hi Bryan

You question peaked the interest of the maths nerd in me

I found this quite interesting: http://peteward.com/ballistic.calc.htm

You have to manually factor in the fact that a heavier arrow leaves the bow at a slower speed, but it gives you some idea.

edit:
After plugging some numbers in, a 500 grain arrow might hit 2 inches lower than a 450 grain arrow from the same bow shooting 20 yards, but at 50 yards, that blows out to around 12 inches lower.

[Stickbow Hunter]

Bryan,

As has already been said it will depend on what distances you are shooting. I personally make my sets of arras within a 20 gr spread. When I make up new sets however they can vary from the other last by another 20 grains but it makes negligible difference at the distances I shoot (out to 30 m on the field course).

In the old days when I shot ABA rounds (roughly out to around 48m from memory) we never even spined or weighed our arras and still got pretty good results. We would just buy our shafts in 100 lots at the spine weight we wanted. I can tell you now that the spine and physical weights did vary a lot.

Jeff

[bryan]

Thanks for the input. I can see how at long ranges it will make a difference however my ranges won't often exceed 30m at the range and not more than 20m in the field. Thought that it might vary more with the weight than it appears to even at 20m.

[Fraser]

I'll through in my 2 cents worth,
1.if you shoot a longbow by now you've probably noticed that the heavier the arrow the less the hand shock, ie more energy goes into the heavier arrow. Don't how this applies to recurves.

2. The heavier the arrow the slower it bleeds off speed.

3. When shooting lite bows 60# and under 100gr makes a huge difference at 48m, when you fast forward to heavy bows of 90# and above 100gr makes little difference at 48m. The ultimate example is artillery pieces, a 105mm howitzer firing standard ammo has a max range of about 9km, and a 155mm howitzer firing standard ammo has a max range of about 18km. Both have similar velocities, it all comes down to the bigger heavier shell losing velocity slower than the smaller one.

Fraser.

[GrahameA]

Afternoon

I was wondering how much arrow weight variation people find acceptable for accurate shooting? This question comes about after I recently made 20 odd bamboo arrows with fields points. I weighed them all and bunch them in groups 530gr, 570gr, 600gr. All arrows with in 10grs of each group so the biggest variation is 524gr to 609gr. I marked each arrow with its respective group however at the range I can't notice a difference between weights. It seems no matter what weight they are I still seem to use the same point of aim and achieve 5inch groups at 20m( all arrow rights in that same group ). So at what variation does it make a difference?

How accurate do you want to shoot??

If you are shooting Indoor and if you take out the human influence 5" at 20m it is unlikely to set a winning score.

There are a few things to take into account with this stuff.

Assuming a Normal Distribution:=

with a 5" group most of the arrows will be in a smaller group
similarly if you go with +/- 10 grains most of the arrows will probably be within +/- 7 grains

The faster the mean arrow velocity the less the time of flight and the less the variation in vertical hit.

The correlation between Arrow Mass and Arrow Velocity also varies in that as you increase the arrow mass whilst the exit velocity will go down (due to the increased mass) the bow will shoot more efficiently so their is not a linear correlation. You can also add in that drag is proportional to the square of the velocity so light arrows which shoot faster will have significantly more drag and thus the velocity (time of flight) has an extra few variables in the equation.

Having said all of that if you know the arrow velocity it is easy to approximate the arrow velocity (from the Kinetic Energy) for an arrow of a different mass and thus the time of flight and thus the vertical dispersion for a range of arrow masses - note it is only an approximation but good enough for ranges out to 30m.

Note. If we take the the "Hawkeye" at the NAFA, Caboolture and Gladstone shoot and you are shooting 5" groups at 20m wha do you think your chances of taking the money are?. If we go to the other end of the spectrum and look at the Vegas indoor shoot. If you shoot 3 off perfect 300's you will be amongst the top 20. (Compound Unlimited) which is an indication at the top end how tough the competition is. http://www.nfaa-archery.org/tournaments ... esults.cfm

[matt61]

I did the same as Jeff and made up my woods in bunches with the weight spread of twenty grains between
the lightest and the heaviest.I learnt a good lesson before that,I bought six shafts that had nocks and field points
all ready on and then painted and fletched and crested them all fancy,but they shot crap because there was
one hundred and sixty grains difference between the lightest one and the heaviest one when I got around
to weighing them .Take a bit of time and get them as close as possible,it will make a hell of a difference

[perry]

I went through a stage where I made sure I had as perfectly matched a set of Arrows as was possible and in the end my Form let me down and played a greater role in how accuratly I shot. I have backed off a little on having Arrows that are within a very tight weight variation now as I am not a consistent enough Archer to pick a 20 gr Variation, I still make sure my Arrows are exactly the same Spine but more effort into Form.

You on the right track starting with a lot of Arrow Shafts, shoot them and I'll bet you will find Arrows that group in different area's of the Target because even if you hand plane Shafts from right next to each other in a Board there is could still be a very slight natural variation because Mother Nature plays a hand in growing timber - if you buy your Shafts they could have come from 10 different tree's, see what Shaft group together and there's you set

regards Jacko

[GrahameA]

Hi All.

I went through a stage where I made sure I had as perfectly matched a set of Arrows as was possible and in the end my Form let me down and played a greater role in how accuratly I shot. .....

And there is the issue.

You can match the arrows so that they fly very close to each other and thus would have a very similar point of impact (ie a small group) and all of that work is over-ridden by the archer who is unable to shoot consistently.

Jim Park has done a lot of work using his "Hooter Shooter" and the results tend to indicate that the biggest variable is the "Archer".

IMHO If you build arrows that have characteristics such that they should group reasonably tight (set your own standard) and the results of when they are shot is a bigger group then the issue lies with the archer and not the equipment.

It can be an interesting exercise if you have access to a Chrony to shoot the same arrow a dozen times and take note of the variation in Velocity. Since the same items are being used for every shot the variation must due to the archer.