Spud Shot Distance

[cfrehr]

hi, i want to build a spud gun with a chamber made of 4" pvc 5 feet long, converting to barrel of 2" pvc 10 feet long.....shooting a potato and using hairspray as fuel, how far do you think my potato would go???

[bigbob12345]

Why didnt you just post this in the other topic?
But you still didnt provide enough information. Chamber fan? What are you using for ignition?
But I would expect the potato to go roughly 150-200yards but that is probably overestimating.
There are ballistics calculators out there that would give a more accurate answer.
And I would highly reccomend you cut your chamber down to 2ft and keep your barrel the same...that would give you a nice C:B

[SpudFarm]

bob: his ratio is 1:1.. (i atleast think so)

i think it will get about 300yards if you put some effort into it.

[bigbob12345]

bob: his ratio is 1:1.. (i atleast think so)

4in pipe does not have twice the volume of 2in pipe, it has about 4x the volume.
4in pipe has an ID of 3.998, so 3.998/2=1.999.....1.999*1.999=3.996
3.996*60(in)=239.76*3.14=752.846ci
2in pipe has an ID of 2.049, so 2.049/2=1.0245....1.0245*1.0245=1.0496
1.0496*120(in)=125.952*3.14=395.489ci
which gives a ratio of 1.9:1, not excactly ideal

but shorten that chamber two 2ft and look what happens.
3.996*24(in)=95.904*3.14=301.138ci
And it comes out with a ratio of 0.76:1, ideal

[SpudFarm]

oh dude..
i allways talk before i do the maths

what he can do is make the barrel longer and keep the chamber and get more performance

[bigbob12345]

what he can do is make the barrel longer and keep the chamber and get more performance

Im not sure that he wants a 20ft barrel

[SpudFarm]

i uses it

[bigbob12345]

Doubt its much fun to lugg around though

[SpudFarm]

not that bad if it is of PVC so you can acctualy lift it by your self

[bigbob12345]

just out of curiousity...How heavy is your hybrid barrel(in lb's)?

If he put together a gun with a 5ft 4in chamber and a 20ft 2in barrel it would weight around 100lb's or more. Im thinking cfrehr's gun wont be a handheld

[starman]

hi, i want to build a spud gun with a chamber made of 4" pvc 5 feet long, converting to barrel of 2" pvc 10 feet long.....shooting a potato and using hairspray as fuel, how far do you think my potato would go???

If you're planning to shoot spuds only, you're wasting your time and materials on such a large gun. If the potato doesn't vaporize, you won't get significantly more distance than if you built a more standard size. Also, if you did use a chamber that big, you should put a fan or 2 in there just to circulate the fuel evenly.

Consider scaling things down to say a 2' chamber and 5' barrel. That's still considered a large gun and it will be much more portable....and you'll get the same distance performance with a potato...and a respectable 1.6:1 c:b ratio.

[SpudFarm]

60 kilograms = 132.277357 pounds


i bet the PVC barrel is lighter than you said

[bigbob12345]

Wow, quite heavy.
I bet it weighs atleast 200lbs with a the chamber and fuel meter and everything attatched though.

And I meant the entire PVC gun put together including the chamber.

[SpudFarm]

ok. but we stop talking about this. i talk to you on msn

[jimmy101]

...
which gives a ratio of 1.9:1, not excactly ideal

but shorten that chamber two 2ft and look what happens.
3.996*24(in)=95.904*3.14=301.138ci
And it comes out with a ratio of 0.76:1, ideal

Yes, and the 0.76 CB gun will probably have a lower muzzle velocity than the 1.9 CB gun, if the spud survives. HGDT says (guessed at some things about the gun) the 1.9 CB gun will have a muzzle velocity of 670 FPS, the 0.76 CB gun 520 FPS.

If you want to increase the performance of the gun it needs a longer barrel. Making the chamber smaller will decrease performance.