Medieval style crossbow

[stuckinthemud]

Just about finished my 15th century style crossbow. Lots going on in this, carved antler inlays, cow bone spine and bolt rest, antler nut, water buffalo horn inlay with v-tool engraving filled with varnish/charcoal mastic.  The prod is yew/sinew 75lb at 8.5 inch, but has been tested out to 110 at 11 inches. The string needs the centre serving and then the whole thing needs snagging, a few hours pottering about on it but basically its
all done.

[Del the cat]

Wow, nice work
Awaiting the performance report with interest! 
Del

[bjrogg]

Sure is a looker. I’m interested to know how it performs to.
Bjrogg

[stuckinthemud]

Thanks both, performance in this de-tuned set-up is not spectacular,  can't give you any figures as I don't have a chrono, and I don't have a place to shoot.  Theory suggests it should be about the same as a 30lb bow and that seems about right.  I will see if I can get some meaningful figures off an audio stopwatch.  When I was tillering the bow and I took it to full stretch, the sinew was really working and the performance at 110lb at 11 inches was huge, the bow just came alive.  Maybe one day I'll put a bigger prod in this tiller and make a new tiller for this prod.  I have a reflexed yew prod waiting for sinew but my supplier keeps letting me down.

[bassman211]

Really nice work on your crossbow. It has bling.

[bassman211]

Really nice work on your crossbow. It has bling.

[stuckinthemud]

Bling, yup  that 's what this one is all about.  Managed 3 readings on a 5m distance, bare shaft 14inch bamboo shaft.  Speed was .165, .175 and .185, so average .175 to travel 5m.  But that doesn't allow for the sound to return to the mic.  Anyone able to convert that to fps?

[Del the cat]

Bling, yup  that 's what this one is all about.  Managed 3 readings on a 5m distance, bare shaft 14inch bamboo shaft.  Speed was .165, .175 and .185, so average .175 to travel 5m.  But that doesn't allow for the sound to return to the mic.  Anyone able to convert that to fps?

I make that 96.5 fps...
5m=16.404ft in .17 secs
so that's 1640.4 ft in 17 secs
so that's 1640.4/17 =96.5 fps
I think that shows why they needed those huge draw weights...
Del

[stuckinthemud]

Mmmm, disappointing but not surprising   hopefully as the prod loosens up and I tune things a little bit it might gain a few fps, but yes, they are inefficient.  A power stroke of 5  inches can only do so much

[Kidder]

That’s some beautiful carving you did there! I had always equated the extra draw weight of a crossbow with extra arrow speed, but as soon as you mentioned the draw stroke it makes perfect sense. That said I still wouldn’t stand in front of it!

[stuckinthemud]

I think the huge draw weight was more about throwing a heavy bolt with low speed and high inertia, I saw a video one time where a bolt looked like it was drifting down hill but when it hit the target it kinda picked it up and just kept on going

[Gimlis Ghost]

The CB looks great. Performance is still sufficient for small game.

I think the huge draw weight was more about throwing a heavy bolt with low speed and high inertia

My thoughts exactly. The limbs can only react so fast and no faster so attempting to achieve high velocity by means of extreme draw weights is not going to be possible as long as a simple prod is used, the limits of the materials are the limiting factor. To get a great increase in velocity the modern compound type set up it a necessity.

PS
Have you seen the Swiss target crossbows that mimic rifling by having deep spiral grooves cut into a steel shaft which is inserted into a cog shaped hole in the center of a steel prod?
The teeth of the hole engage the grooves on the bolt body spinning the bolt for stability when fired.

They fire into a thick wooden target and to ease removal of the bolt a spanner is slipped over the end of the bolt. Instead of a conventional head the head end of the bolt is threaded like a coarse wood screw. In turning the bolt with the spanner it backs out of the wood.
The bolt is the most difficult part to make, so they usually only use a single bolt custom fitted to their cross bow for all shooting.

Don't know if this method is still in use, I read of it in the 1960's and have heard nothing of it since then.

[stuckinthemud]

Not heard of that one,  presumably they don't use fletchings?  Seems like a lot of work when offsetting fletchings produce the same effect.   Interesting fact, it was compulsory by law, I think in 16th century Sweden to make bolts spin in flight to improvd accuracy

[Gimlis Ghost]

Seems to a have been a very limited competition type thing, very few contestants at any time.
The bolt to bolt results were so precise most groups were one holers, tighter than most firearms could deliver at the time.
The Crossbows were very heavy bench mounted pieces, like a bench rest rifle.

I don't think these had any practical purpose beyond competition.

[bownarra]

Just use helical fletching.....
You should try making a Chinese style crossbow with a long powerstroke. They are quite something. I made one with a 21" powerstroke, 110#, and that thing really puts them out.....5 shot groups with the bolts/arrows touching as well. My plan was to make a short as possible hornbow for it but never got around to it. At the moment it has got a boo backed ipe bow.