marble cannon

[RickB]

Hi all,

After some advice i want to build a marble firering cannon.
and was after some advice on best route to take.

I might be abit optomistic but after a shooting range of around 4oo meters is this possible?

I have made combustion and pneumatic cannons in the past but have fired larger items than a marble.

was thinking of a small hybrid cannon and this is where i need advice, what would be the best design to use combustion chamber size and barrel size and lenght ect.

also would i be able to use copper pipe for combustion chamber for lower pressures?

any help appriectiated

[DYI]

This all hinges on your definitions of "marble" and "firing range". If you mean "ball made of some kind of glass of less than 2" diameter" and "maximum distance to impact when fired over a flat, level surface", respectively, then yes, it is possible. Get HGDT and use its external ballistics calculator, or write a simple one of your own. It took me about 5 minutes to write the one I used to answer your question, because I didn't have one close at hand.

As to design: that will depend entirely upon the performance you aim to achieve. With a 15mm diameter marble having a mass of 4.4g, 400m is a long way, requiring a muzzle speed in the neighbourhood of 800m/s, for a total energy of 1.4kJ. That can certainly be done, but copper pipe would not be up to the required pressure unless the barrel was very long.

HGDT is primarily an internal ballistics calculator, and can be used to approximately predict the performance of the gun you want to design. It is also extremely easy to use, has a nice GUI, and requires no programming or other skills. In the performance regime you're looking at, it will tend to predict high, perhaps as much as 25% high on the velocity, based on my (admittedly limited but very well instrumented) experiments to date.

[jimmy101]

400m is a really long way for a homemade weapon. (Anything that can launch a projectile that far is definitely classified as a weapon.) At that range to actually hit a target smaller than say a small mountain will require a rifled barrel. A smooth bore firing a round projectile is going to be extremely inaccurate at 400m. For comparison the http://en.wikipedia.org/wiki/Brown_Bess fired an 0.71" round ball from a smooth bore with an effective range of only about 100 yards.

[bravootome]

[quote="jimmy101"]400m is a really long way for a homemade weapon. (Anything that can launch a projectile that far is definitely classified as a weapon.)

I bet a steel bb can travel 400 m even at low power set with a decent homemade airrifle and a good scope. It may hit a car size target after lots and lots of tests....

[RickB]

seams like a inpossible task lol,

what range would you expect to see from a marble size projectile?

[DYI]

The question here is really whether he's asking about maximum range or effective range. Obviously getting 400m effective range with a ball of any sort is a hard ask indeed, but simply reaching that distance is feasible, as I pointed out above. Also, I have to challenge your definition of a launcher that energetic as a "weapon" - a weapon needs to be usable as such. Most hybrids would struggle to fit that bill, given the accuracy, weight, reload time, and general lack of ergonomics.

RickB: you didn't read my first post in here, did you?

[jimmy101]

DYI

Given the rather limited description in the OP the device qualifies as a weapon. I don't think the kid is thinking about a Vera sized device, or even a device to big to be hand held. Reload time is irrelevant, accuracy is irrelevant, poor ergonomics are irrelevant. Can you hold it in your hands and fire it (once) at a person and do damage to that person? I think in most jurisdictions that is all that is required for the definition of a "weapon". If the device lacks any utility other than launching a small object at high speed i think most cops would call it a "weapon". (So a nail gun isn't a weapon since it has other utilities.) There are a fair number of hybrids on these pages that definitely qualify as "weapons".

[jimmy101]

I bet a steel bb can travel 400 m even at low power set with a decent homemade air rifle and a good scope. It may hit a car size target after lots and lots of tests....

I think 400m is pushing it, even as a maximum range. According to HGDT's ballistic calculator (I know, not the best one out there) a standard steel 0.17" BB at Mach 1.5 wouldn't make it 400m.

[DYI]

Reload time is irrelevant, accuracy is irrelevant, poor ergonomics are irrelevant. Can you hold it in your hands and fire it (once) at a person and do damage to that person? I think in most jurisdictions that is all that is required for the definition of a "weapon". If the device lacks any utility other than launching a small object at high speed i think most cops would call it a "weapon".

Oxford defines a weapon as "a thing designed or used for inflicting bodily harm or physical damage". Doesn't sound like the OP has implied anything of the sort. If we start speaking in legal terms around here, nobody's going to get anything done

I think 400m is pushing it, even as a maximum range. According to HGDT's ballistic calculator (I know, not the best one out there) a standard steel 0.17" BB at Mach 1.5 wouldn't make it 400m.

Oh, I don't know about that. For a 3/8" steel ball, the speed required for a maximum range of 400m is no more than 250m/s. Fast for a pneumatic, but not extreme by any standards we're used to on here. If we use a 1/4" tungsten carbide ball, or a 1/2" steel ball, we can exceed 400m maximum range with a muzzle velocity under 150m/s.

[bravootome]

seams like a inpossible task lol,

what range would you expect to see from a marble size projectile?

Well if you shoot supersonic..........look on youtube someone shoots golfballs with 1550 fps, cant find th link now..