Crossbow Bolts and Warbow Arrows

There's been a lot of interweb activity due to Coronavirus lockdown, much of it has been an irritating waste of space, but there have been some sensible discussions.

One chap was questioning if warbow arrows were sorted in spine in any way... some people chipped in asking why "random arrows" would be all put in a barrel together. Of course that sort of comment is weighted to support his own position... the arrows were not "random" they were made to some sort of specification (albeit, maybe not a written one) in that they would have been suitable for warbows, say 3/8 - 1/2" shafts, big long fletchings (3 per arrow), heavy head, between 28 and 32" long. We know from documentary evidence that the shafts and heads were not necessarily assembled where they were made, so sheaves of shafts and barrels of heads would be sent up to the Tower of London. maybe one bloke cut all of his shafts the same length, maybe they were trimmed to length when they were made into arrows.
The point is we shouldn't jump to conclusions. What we do know is that measuring the spine of an arrow shaft by hanging weights on it and doing arithmetic is a modern idea. Now that doesn't mean that a native making arrows for his bow didn't flex 'em to select those he liked best or flew best, but, spine wasn't actually "measured"...
Ah, but does it even matter?... The bloke who asked the question had no real experience, and was just quoting what he'd read (sigh). So, as well as stating my experience I thought I'd better back it up with an actual experiment.
Does the spine of a Warbow arrow matter? Well we know they fly pretty well out of heavy warbows, but what happens if you shoot one out of a 70#@32" bow? It should theoretically be over stiff in terms of static spine*. Then if we shoot a 5/16" 30"arrow of 40-45 spine from the same bow what happens? Does the sky fall in?
Well the heavy arrow hits the boss square on at 10 yards having straightened out already due to the heavy head and big fletchings. The light arrow is still flexing as it hits at 10 yards, but they both fly in a perfectly usable manner. (see pic)

To keep me busy I've been turning up some 3/8" points for my heavy 275# repro "Light Sporting Crossbow" It uses up some odd Ash shafts I have lying around and some of the feathers I picked up the other year. I'll post some pics and video when I test them in the crossbow.
I've finished one bolt and tested it from the crossbow. It flew nicely at 10 yards, I also checked the spin by lobbing it up in the air underarm and watch it spin as it fell back down. The 2 fletchings are slightly offset to enhance their natural curve to induce spin. You can see on the pic of the fletching jig I have stuck a bit of white card under the front edge of the clip that holds the fletch, that just lifts it a tad.


* For those who don't understand the difference between static spine and dynamic spine.
Static spine is simply how the shaft flexes when a weigh is hung from it's centre... but when it is shot from a bow there are other factors like the weight of the head... if the head is very light, there is very little to stop the arrow accelerating, so there is little force bending it. With a heavy head, there is lots of inertia, so rather than accelerate forwards the arrow will flex.
Taking this to the limit, and a 50 spine arrow with a 15 grain head can be shot from a warbow. Conversely an infinitely heavy head (which is simulated when you over draw and jam the point of the arrow into the belly of the bow) will cause the same 50 spine shaft to explode! The length of shaft also effect dynamic spine...if you pick up a 3 foot length of scaffold pole and give it a shake it feels rigid. If you pick up a 20 foot length holding it at the centre and jerk you hand up and down you can feel it flexing.