LARP crossbow from UK

First topic message reminder :

Hey folks!

I'm John, a Biomedical sciences student from Durham in the UK. I've recently gained an interest in crossbow building after a pretty thorough foray into the modification and building of safe NERF weaponry for our university's Assassins society. I basically covered most of what can be done with that, and now I'm going for something a little prettier and more classic; the crossbow.

I'm intending to eventually build some real, high-poundage bows for target shooting, but for now my efforts will be geared towards producing replica bows with a strict poundage limit (30lbs at 15" draw) for use in live-action roleplay (LARP) and our Assassins games. These bows will need to look the part, but fit the strict safety guidelines of said societies/groups, and will need to fire soft-headed, front-heavy safety bolts (e.g. http://www.thevikingstore.co.uk/larp-crossbow-bolt-flat-headed-6115-p.asp).

At the moment I'm building my prototype bow, upon which future efforts will be based. The stock will be made from laminated sapele timber, the roller-nut made from the same, and a hand-forged (albeit with a blowtorch) tickler. The prodd will be carbon fibre, wrapped in cloth to avoid danger from limb failure.

I've ran into the issue of how to calculate the length of prodd I'll need in order to reach the desired poundage (30lbs to reiterate) at the correct draw length (15"), as I'm a little limited in terms of the material I have to hand, and so have little room to experiment. I'm planning to use two lengths of carbon fibre strip, one shorter than the other, to make a laminated prodd and even out the work done between the tips and centre of the prodd.

I'd be grateful for any suggestions anyone might have!

Regeis wrote:I get the feeling that I should make the tickler more slender... opinions?

Make it metal. Buy a peace of 10mm round. And that should be easy enough to make a tickler bending it cold.

Yes... It'd make it more slender. Take a look at the wooden tickler in my Avatar picture or on my newest build here" https://thearbalistguild.forumotion.com/t945-loose-laminate-pinlock-build#9107

Thanks Kenh; how did you go about carving down that particular shape? I used a combination of sawing and chiselling away waste, block and compass planes and files, but it was slow going.

I used a combination of sawing out the basic shape matching the underside of the tiller, then sanding to the final shape and dimensions using an inverted belt sander. After that was a couple grades of sanding block and I was done.

With the lever of that arm being so long, there is little pressure being applied. till I made sure the grain of the wood was running down the length of the tickler.

Thanks Kenh; I guess I'll keep going with the files, maybe get hold of some rougher rasps, as I try not to use power tools where I can. The hand-drill in my pictures was the exception as I wanted a clean hole through the tickler, and I thought a brace and bit would chip or tear the knot I put the hole through.

I'll see what I can do with the files, sandpaper and various other means and make the tickler more slender.

So I got hold of a 15lb children's fibreglass bow; looking at it, it was essentially one of those tension bars you used in your build, KenH, but with moulded plastic knocks and riser added to it; turns out it's about the cheapest way for me to get hold of fibreglass bar in the UK =/

I cut away at the riser until it became loose enough to come off the fibreglass, and slipped it off. The knocks aren't glued, so I'll keep them and glue them on the final build.

It's now a case of building a tillering jig and cutting the bow shorter until it pulls 30lbs at 15" draw. I'm not sure how I'm going to make the thing tiller evenly, as I'm pretty sure that adding a second layer will make the draw too heavy; I may have to just leave the middle taking more of the pressure than the ends, but I'm making progress!

Good deal! Yeah... I'd only tiller to weight by length reduction. I recently built a takedown longbow for my girlfriend's daughter and the project involved shortening an existing wood bow of known draw weight.

After a bunch of hunting about I found the statement that "a 1% reduction in long bow length mean a
5% increase in draw weight."

So if your 15# bow is, say 80 cm long, then reducing its overall length by 1 cm will increase the weight by about 5% or .75# The Rule of Thumb worked out exactly right in my case; it should in yours too.

I have been following this and here is something that has puzzled me for a while

Regeis wrote:t's now a case of building a tillering jig and cutting the bow shorter until it pulls 30lbs at 15" draw.

Why do you need to maximize the power?
I understood you will be shooting real people with boffer bolts.
That limit is there for your own safety.


Have you tried shooting your bow ? Maybe it allready has adequate performance. You should be able launch crossbow bolts from 15# bow with bare fingers and pinch release.

In any case , shouldn't you go for 25#14" not 30#15", in order to be on the safe side ?

Nerd -- I suspect what he wants to do is use the maximum draw weight his rules allow, rather than say performance. Those boffer bolts are not light, that's for sure....

Exactly right, kenh; the bolts weigh about 5g less than a tennis ball, so I'd like to eke out every bit of power I can so that it's easier to aim and hit people who're trying to hit me with swords =P

I'll likely leave it a little below power so that the refs have no reason to disallow it, even if variations in moisture and weather affect the poundage, though.