Heavy hitting crossbow

Hello From SW Florida USA, been reading this forum for a few days now an love it.

The reason I came here is I'm trying to plan a crossbow build that will give me the best possible hard target penetration.

Currently I'm using a 150lb barnett (fiberglass prod no cams) and a 60lb bear (modern split limb compound) with modern "big game" fiberglass bowfishing arrows and the power/penetration is completely unsuitable, my arrows are bouncing off.

What I'm hunting is alligators (from a boat with license/tags) and they have extremely heavy scales over most of their back. Now the proper way to shoot one is to get a broadside shot and hit them low in the neck/side where the skin is soft but this isn't always possible and many times the animal dives before I can get a shot like that.

So I want to build or modify a crossbow that will penetrate about half an inch of solid bone scale on the head or back of an alligator. The normal shot is 3-8 meters so it doesn't need to shoot very flat just penetrate extremely well.

I'm open to about any design from the oldest to newest even a torsion or rubber powered bow and I don't mind spending some time or money to build what I need. Draw weight can be about anything and the bow can be about any size or weight however it must be managable enough to fire it handheld, mounting it on the boat like a whaling harpoon is not legal.

I have a basic shop with a lathe, mill, grinders, welders and normal woodworking tools saws/drills/routers.

To get more power two main ingredients are draw length and draw weight. Do you know how much energy you want? Several modern crossbows shoot over 400 FPS with relatively light arrows. There is a man in Canada I believe who makes "industrial" crossbows for forestry and rescue work that can shoot a 1000 grain arrow at almost 500 FPS. I will try and find a link to it maybe you can get ideas from that crossbow.

Todd

Here is a youtube video of that crossbow:

https://www.youtube.com/watch?v=cxuEi0uZJ7g


Todd

I really don't know how heavy it needs to be, the only trustworthy reports I've heard of punching alligator back armor without a firearm involved using a handheld pole like a jousting lance from a moving boat or using an iron water pipe as a handheld harpoon. I've talked to a lot of guides and I'm pretty sure no commercial deer bow/crossbow will punch back armor.

I really need a heavy bolt so it can fly straight into the water and also pull the a good sized line behind it. I want to get away from the normal 400lb "big game" bowfishing line and use a much heavier dyneema rope that will resist damage and give me something better to hold onto. I'm thinking the bolt should be as heavy as possible, perpaps half a pound or even a pound if it will shoot flat enough to hit something at 20-30 feet.

My speargun spear (2lb?) is too heavy, it has such a horrible trajectory that it's not practical but then the speargun doesn't have a lot of power either.

Is there some limit to the draw length on a normal steel prod without cams, can you simply make the prod 4-5' long or would it get too heavy? I get that draw length and weight are both important factors but I don't know which one I should be focusing on. My first thought was to make a short steel prod in the 800lb range and shoot heavy steel bolts but I'm open to anything.

Too heavy shouldn't be a problem, usually they are in 10' or more of water when I shoot them so if the bolt goes all the way through that is fine by me.

Draw length on a steel prod is limited by the physical properties of steel itself.  A long prod not only will be heavy, but unwieldy as well.

Where are you in SW Florida?  I'm in Fort Myers... live at the City Yacht Basin at the foot of Lee St.

Look at my loose-laminate pinlock build here:
https://thearbalistguild.forumotion.com/t945-loose-laminate-pinlock-build?highlight=pinlock

A fiberglass tension bar, multi-laminate build may be a viable solution.  The fiberglass is also not bothered by exposure to salt and water the way steel is.  You may want a different action, too, although I've seen Norwegian whaling harpoon crossbows that used a Skane pinlock.  

I also think you need to do some moderately scientific tests with fresh gator hide and a controlled pressure press to determine the amount of penetration energy required.    Even working with fresh hide and a couple different firearms will give you some useful penetration data -- will a .22 rifle/pistol reliably penetrate?  What about a low power .38 Special round from a 6" pistol?  Energy data for those rounds at your distance can be easily converted and related to crossbow penetration.

I'm in Fort Myers as well, as a matter of fact my shop is only 3 miles from the yacht basin.

Scientific testing may prove difficult as I didn't get tags this year, my plan is to go for extreme overkill and test it on something like several layers of plywood. I know I can build an air cannot to shoot completely though an alligator but I want a weapon that won't confuse the game wardens.

You might be over estimating your needs, here is a thread on another forum with people using recurve bows.

http://leatherwall.bowsite.com/tf/lw/thread2.cfm?forum=23&threadid=252024&messages=39&CATEGORY=9

Todd

Interesting reading Todd.  Those guys weren't making back  shots though.  The back armor on a gator is at least twice as thick as the side armor, and is much larger plates where a tip can slide off more readily.  

I don't honestly believe that 1776 is gonna need anything more than say 250-300# draw (equivalent to a 64-75# 'long' bow).  Gator armor isn't like 1/2" plywood, probably not as tough as 1/4" ply.  But it is flexible, which is why I suggested test shooting real gator back armor taped to a pork roast.

That light equipment can land big gators but it also accounts for most of the losses, it's really no different than trying to land a bass on 2-4lb line, it can happen but it won't always work out. Also a great deal depends on where and when you are hunting, later in the season or in the higher pressure hunting areas it is much harder to get the perfect soft spot shot on a decent gator.

Using commercial fiberglass arrows modern bows and crossbows cannot punch alligator back armor, I've tried and failed several times and I've talked to a lot of guides as well. In the soft side skin they work fine but you are still dealing with a flimsy arrow and line so the games not over until you get a real harpoon line in them or snare them around the neck.

Seventeen:  are you using standard barbed fishing points on your bolts?  A change to classic bodkin-points (three or four edge, sharp) or even very stout, sharp broadheads should get you more penetration than a round/pointed fishing point.  
When medieval guys wanted to pierce leather they went for broadheads.  For harder armor they used sharp bodkins.  Try 'em. 
Geezer

I use points like this, it's designed to fall off the arrow shaft and lock underneath the skin. I did modify it with a wire leader because even heavy dyneema superbraid doesn't survive being tied directly to a steel tip like in the advertisement picture.

I also have some like this, pretty much a standard fishing point with an improved tip

Interesting discussion. Now I won't be satisfied until I know whether my heavy bodkins, fired from my hardest hitting crossbow, will punch through gator back or not. How much is a gator tag, anyhow?
Gnome

Like most states Florida sticks it to non-residents for hunting licenses, IIRC it's about $1200 for a non-resident gator license. If you really want to go and aren't in a hurry it is cheaper in Georgia but harder to get a tag so you need to apply and lose (probably) for a couple of years to get the "preference points" to win.

Hello there!

I do not have experience in piercing something but I do have some points concerning this discussion:

-If you hit a scale with an low angle there can be even with the most powerful crossbow, less guarantee to penetrate it. So keep your shots in a good angle. 6-8m on a flat gators back can definetely be no good angle! there is a good reason why modern tanks have flat angled surfaces!!

- Since force ist resulting from projectilemass and speed(acceleration)
You will want to use a prod as powerful and fast, as it can be with a relatively long power stroke to improve projectile speed.

Unfortunately Steel ist limited in it´s "reset" speed due to the high specific weight and comes with shorter power strokes the stronger it will be. The longer the prod the longer the stroke, but the heavier/slower the prod. In conclusion you will get a strong prod with a relatively massive boltweight but slower than modern type materials.

Couple of months ago I had the idea to build a relatively massive prod made of glued GRP strands oriented on the diameters of horn/sinew compound with benefit of modern materials some day.

My thesis is, that due to the dynamic of strain and compensation combined in the material it could result in a flexible (long stroke) relatively lightweight and VERY powerful prod.

More advanced option is kenh´s solution of constructing multi layer designs, but i think this is very expensive at a certain point.

I do not see big differences between your points and the design of for example a heavy war or tudor bodkin but as mentioned above penetration depends a lot on projectile mass which obviously seems to me very low.

My question is, you do not want to kill with the tiny boltheads, do you?
I assume it is just for pulling the gator closer to you?

Rizzar

It sounds a bit like you want something akin to a siege weapon mounted like a harpoon?  

On this thread  -  https://thearbalistguild.forumotion.com/t1029p15-rules-of-thumb-on-the-optimal-bolt-weight

...some members shared ideas about the best bolt weight for my steel prod crossbow.  There are a few insights on what makes up the kinetic energy of a bolt and what prod/ bolt weight will pack the most punch. 

You could start with a KE number and reverse engineer a bow but will run into material limitations at some point. 

I found that my 250# steel prod would hit hardest with about a 1000 gn bolt (1/12 mass of prod) but the speed and trajectory loss was too much in my estimation for deer hunting.  I ended up deciding on about 600 gn as a compromise (500 gn may even be better).  However, if your gators are 20 - 30' away - find the optimal KE and the trajectory loss will be negligible.

My gut tells me a 300 - 400 lb steel prod with a 1000 grain bolt would punch through just about anything at 20 feet.

Rizzar wrote:
My question is, you do not want to kill with the tiny boltheads, do you?
I assume it is just for pulling the gator closer to you?

You have to secure them prior to killing, after you wear them down like a fish you bring them near the boat and kill or stun them with a bangstick. Once they are lifeless you tape the jaws up and kill them more absolutely by cutting the spine just behind the head.

Hotspur wrote:It sounds a bit like you want something akin to a siege weapon mounted like a harpoon?

Anything that works but it can't be mounted, it must be hand held to comply with the law. It can weigh 20-30lbs because it only has to be hand held long enough to fire it.

What range is optimum for taking the shot? I guess i was thinking in terms of bow fishing, where it is relatively short and down-angled where a heavy projectile would be an asset. Then I thought, no, wait, that isn't a fish, it's a giant, prehistoric scaly monster that can outswim, outrun, and outbite me. How close do I want to be when I start lobbing darts at it?
Gnome

Gnome,

  Not very close and may I suggest using a harpoon cannon with the word "crossbow" painted on it.

Chaz

You want to be as close as possible if they will allow it, if you can get right up on them and use a handheld harpoon that is ideal because then you have a strong, thick rope to lead them in with. But when they get spooked it gets harder and harder to get in close so you have to switch techniques and use a bow or snatch hook.

Some people are very handy with a handheld harpoon and can throw it and hit something but that isn't my thing.

Am I correct in that installing a very basic set of compound pulleys will double the draw length while halving the weight?

I've been doodling and I've come up with duel steel limbs with cams mounted between them and the bolt firing through the middle of the limbs. Something like 26" 5160 steel prods 5/16 or 3/8" thick 1.5" wide tapered in width down to 1/2" drawn back to 8-10"??? without compound or 16-20"??? with compound. It would seem these prods would be in the 600-700lb range each or preferably half that by using a compound?

My 150lb barnett shoots a 2.3oz (1000 grain) fiberglass fishing arrow plenty flat for my purposes so I'm thinking 10-12oz for the new bolts using the same sort of sliding line attachement, I believe this bolt weight will allow for solid steel bolts towing 4mm dyneema line which would be ideal.

Now one problem that is apparent is tempering my prods, I have a knifemaking furnace (240v paragon 14D) but it only accepts 14" long blades so I can do all the little lock parts but unless there is some way to use 4 short prods I will need to find a swordmaker or someone to temper my prods.

If you're anywhere hear a spring shop they might temper a prod for you.  Or you could use leaf springs and cut them in short cuts and keeping it cool avoid losing the temper.

Or you could go with glass - Gordon Composites Power-Tuff Glass is purpose built for this kind of application.  Fairly cheap from http://www.binghamprojects.com page three/ bottom right of their pdf catalogue (you have to phone for quote).  A couple of billets of this would make a wicked bow. There is a thread about kiwijim's bow here https://thearbalistguild.forumotion.com/t119-new-hunting-crossbow using power-tuff.  You can order pretty much any length, the stuff I got was 2" h x .5" d (smooth one side)for the next project.  You could achieve a monstrous draw weight if so desired.

I still think we can make you a suitable prod from under $20 worth of fiberglass tension bar.

Seventeen76 wrote:Am I correct in that installing a very basic set of compound pulleys will double the draw length while halving the weight?

Square root of 3 (~1.7 )times the length
with 58% of weight.
About approximately. With plain round regular pulleys.

kenh wrote:I still think we can make you a suitable prod from under $20 worth of fiberglass tension bar.

Any idea who sells that material in the lee/collier/charlotte area?

Thanks nerd that is exactly what I needed to know, it sounds like a pair of 600lb prods will give me 700lb at 15-17" of draw if I compound them.

Tropical Fence on Palm Beach Blvd between Miramar and Balboa.  They sell in several lengths.  I bought a 5 ft piece there that cost me $7 and change.

kenhulme at gmail dot com