SpudFiles

I am working on a gun that is not spud gun related. I would like to send info and ask permission to post it here. Who and how do I contact?

If it burns magic powder it's unlikely to be included on the forum, but you can contact PC_GUY, jrrdw, MrCrowley or any of the other moderators by

I've approved it, hopefully he'll post it soon.

MrCrowley wrote:hopefully he'll post it soon.

Sounds promising

yeah, when you say it, it is it

Thanks,
It may be a week or two. I need to finish it and do some testing.

We like having build logs

So what kind of gun is this? Does it use "magic powder"?

No dark magic.

A friend of mine brought a crossbow to work one day and challenged me to build a better one. Well you know todays crossbows are state of the art and have little room for improvement. But I did figure I could make an arrow shooter that was far less bulky than a crossbow with about the same performance. So that was/is my goal. I guess you could call it a "pop gun", but this ain't no kids toy. Im not even sure its going to work, but if it does, I think you guys will like it. And if it doesnt, Ill post it anyway and let you guys rip it.

OK here it is. I thought I could take a spring to do the work of a bow. Just need a strong enough spring. So I used a spring from the front fork of a 250cc motorcycle. I weigh 200 lbs and it takes almost all my weight to compress this spring into the cocked position. I mounted a tension pin on the front of the spring. It sticks out of a grove on the top of the barrel. That way I set an arrow on the grove on top of the barrel. I could also put just about anything in the barrel. Maybe a potato.

Thats the theory. Heres the result.

It works but its lame !!!

Maximum range with various ammo is about 40 ft. I don't understand it. With a spring that strong and 15 inches of travel, I expected allot better than that.

Any theories as to why this thing wont work. Also I put allot of money and time into this, any ideas of what to do with it now.

Wow, that looks really good! I don't understand why you aren't getting great performace either. I think you should add an airtight seal on the front of the spring so it could compress the air in front of it as it travels then maybe you could get better performance? I don't know, it seems like a good system to me :tongue3:

Very nice looking build! Reminiscent of a Mossberg 500

EDIT
lol... it took me a while to realize that it doesn't use air
I am guessing that there is no equalisation hole behind the piston and that hampers performance?

If you can't get the spring concept to work, convert it to an over under HP pneumatic with a captive bolt firing system

My take is the amount of mass of the iron spring is limiting the acceleration in the Force = Mass X acceleration. Mass and acceleration are inversely proportional so much of the energy is spent accelerating the spring and not the projectile. A Cross bow limits the speed of the heavy part (the bow) and most of the speed is concentrated on a low mass part (the string and arrow).

Even air cannons are limited by the speed the spring can expand. Steel springs have higher mass, but not the greater force, hence the lower terminal velocity.

To find the therotical speed of the spring with no projectile, bolt it to something solid and get it to vibrate lengthwise. The period of the frequency remains the same regardless of the amplitude of the ringing. A fully compressed spring will not expand in a shorter time then the resonant time constant of the spring. Adding a mass with a projectile lowers the resonance frequency and thus the final possible velocity.

I hope some of this makes sense. I'll add a math calculation for an example frequency of say 100HZ resonance. A full cycle is expanded and contracted and back. The minimum time of a launch would be 1/4 cycle, or compressed to 1/2 way extended. 100 HZ is 10 ms. 1/4 cycle is 2.5 ms.

I have considered a launcher using a spring but with a 4:1 pulley so the light string can be used much like a crossbow, but with a coiled spring.

The machining is fantastic. It looks great.