BlackBrook

What Spine wooden arrow will I need?

 

This question is frequently asked, but it’s one I’m reluctant to answer in full; even when we know the bow’s draw weight, there’re still quite a few variables involved.

 

Like: actual draw weight (different to the bow’s draw weight), actual draw length, arrow length, arrow weight, pile weight, how good is your loose? and so on.

 

As a very basic rule of thumb you can add 5 to 7lb (if not more) to the bow’s draw weight and you have a good starting point. 
 
ie, 40lb bow weight @ 28" (AMO)  =45 to 50lb spine, if your actual draw length is nearer 27" than  28" then go 2lb weaker, if its 29" go 2lb stiffer.
 But I stress that it’s a very rough guide so please don’t rush out and buy three dozen arrow shafts just yet!

 

The advice I do like to give is; go and beg, borrow or steal arrows from your fellow club mates to get a good idea what arrow might work for you.

 

It’s very tempting to try and shoot light weight, small diameter arrows such as 5/16” dia shafts from (say) a 45lb (when drawn to 28”) Zeta or Hunter.  Some may get away with it but most won’t!  You are more likely to need an 11/32” dia shaft.

 

My personal choice is to shoot 11/32” diameter POC shafts cut 1” longer than my actual draw length, the spine to be 8 to 10lb heavier than the actual draw weight and to have at least 100 grain piles fitted.

My usual POC shaft stockist supplies me with a fairly consistent shaft weight.

These arrows average out at 440 grain all up weight which is about right for my 47lb bow.
This is just above average "Grain Per Pound" the minimum is 8 grain. (.51 grams)
ie, if your actual draw weight is 40lb, times 8 grain = Minimum arrow weight of 320 grain (20.7 grams)

Generally I have found this arrow set up to work well with Zeta C, Sigma C and my recurve bows.

 

Buying GOOD shafts can be a pain!  Talk to the guys that win comps a lot to see where they buy theirs.  If you are going to play this game properly, you’ll need your arrows to be as closely matched to each other as possible, so go and select your shafts yourself using a spine jig and grain scales.  If the shop hasn’t got these tools for you to use then maybe they aren’t playing their game too well!

 

The dynamics of arrow flight is fascinating to me.  Recently I stumbled across this little program; Dynamic Spine Calculator by Stu Miller Archery.  It may help you understand what changes the dynamic spine of your arrow and what your bow spine requirements are.

When I get round to it I’ll contact the writer to see if I can include it on this site as a download.