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new to spud guns some help or advice please

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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new to spud guns some help or advice please

Unread postAuthor: Daviator » Sun Mar 04, 2012 11:29 pm

i built my first gun to shoot golf balls, it worked pretty good. but now im looking to shoot faster and further. id like to build a gun made of steel and use acetylene and oxygen for the fuel. id also like to make it a break barrel, im planning on getting the barrel rifled, so i can shoot projectiles nice and straight.

ive seen some conflicting info on c:b ratios and have used the hgdt tool but i don't quite understand what im supposed to do with the fan and such to give me a accurate fps estimate. since i dont plan on having a fan in it.

as far as the gun design goes it will be square tubing 3"x3" with a 5' barrel 1.5" diameter, to make it break barrel i was thinking using a hinge on the bottom of the square tubing and three cam lever style clamps welded to the other tree sides with a rubber gasket in between the two pieces of steel to seal it.

what thickness of steel would be ideal/safe to make this out of? does the rubber gasket sound like a death trap?

here is a video of someone's gun which is the same design im looking for, only his doesnt have the break barrel

http://www.youtube.com/watch?v=SzL-yGcJG-w


any help would be greatly appreciated
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Re: new to spud guns some help or advice please

Unread postAuthor: jackssmirkingrevenge » Mon Mar 05, 2012 1:37 am

Welcome to the forum :)

Daviator wrote:square tubing


... should NEVER be used as a pressure vessel.

It will rip apart at the corners.

Especially with

acetylene and oxygen for the fuel


Why are you set on a break barrel? a breech sleeve sounds like it would be a more practical idea if you want to muzzle load as suggested here.

Image

Image

Image

http://www.youtube.com/watch?v=SzL-yGcJG-w


Surprisingly little recoil for the claimed 2000 fps, hmmm...

ive seen some conflicting info on c:b ratios and have used the hgdt tool but i don't quite understand what im supposed to do with the fan and such to give me a accurate fps estimate. since i dont plan on having a fan in it.


Set the fan flow or diameter to zero.
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Unread postAuthor: Daviator » Mon Mar 05, 2012 1:47 am

the reason for the break barrel would be the rifling. i plan on making wooden projectiles to fit the barrel. wouldn't muzzle loading with the rifling mess up the projectile prior to firing ? For a breach load, would you make that somewhat similar to the picture you posted above, if you were using steel?
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Unread postAuthor: Crna Legija » Mon Mar 05, 2012 2:03 am

id go coax for breach loading you have the barrel extent about 1/2 way into your chamber so you can unscrew the cap to vent and load via that same fitting.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 05, 2012 2:13 am

Daviator wrote:the reason for the break barrel would be the rifling. i plan on making wooden projectiles to fit the barrel. wouldn't muzzle loading with the rifling mess up the projectile prior to firing ? For a breach load, would you make that somewhat similar to the picture you posted above, if you were using steel?


http://en.wikipedia.org/wiki/Muzzle-loading_rifle

Nothing fundamentally wrong with muzzle loading in a rifled barrel.

Why wooden projectiles though? Poor sectional density will not give you the best accuracy.

You can also be accurate without rifling as long as your projectiles are aerodynamically stable (ie with the centre of gravity forward of the centre of pressure) like the rounds sold by our benevolent sponsors.
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Unread postAuthor: Daviator » Mon Mar 05, 2012 3:06 am

the wood because i have access to a lathe and i was thinking of drilling out the center and pouring in a bit of lead in to give it weight forward then sealing the back end up with hot glue. 6$ a round is a bit rich for me :cry:
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Unread postAuthor: MrCrowley » Mon Mar 05, 2012 3:11 am

So are you expecting 2000fps golf balls from this design? Like JSR, I'm doubtful the cannon in the linked video was achieving such high velocities but the video wasn't exactly descriptive so I can't say much more without information from the builder.

With a modest sized 10x propane or MAPP gas hybrid cannon, 1400fps is quite feasible.
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Unread postAuthor: Daltonultra » Mon Mar 05, 2012 4:12 am

2000fps my fat, white, hairy... umm. 2000fps is the range of .30 caliber high-power rifles that leaves bruises on your shoulder if you're not tucked right. With the weight of a golf ball going downrange at 2000fps, that guy would have EATEN the cannon sitting behind it like that.

His distance claims are reasonable enough, as is the idea that he put one through a car hood, but his velocity claim is pure BS.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 05, 2012 4:14 am

Daviator wrote:the wood because i have access to a lathe and i was thinking of drilling out the center and pouring in a bit of lead in to give it weight forward then sealing the back end up with hot glue. 6$ a round is a bit rich for me :cry:


Drilling out the base and putting weight in the front will definitely give you more stability, a la shotgun slug:

Image

Done well, you won't need rifling.

Maybe machine yourself a nice mouldlike these folks :)

I'm doubtful the cannon in the linked video was achieving such high velocities but the video wasn't exactly descriptive so I can't say much more without information from the builder.


In theory injecting oxygen and acetylene you can have a "hybrid" mix with a fuel that is significantly more energetic than propane, but still 2000 fps is slightly optimistic.
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Unread postAuthor: MrCrowley » Mon Mar 05, 2012 4:25 am

jackssmirkingrevenge wrote:In theory injecting oxygen and acetylene you can have a "hybrid" mix with a fuel that is significantly more energetic than propane, but still 2000 fps is slightly optimistic.
Yeah hence my reservations about calling it a straight lie, it seemed unlikely he was running it at anything higher than atmospheric pressures (didn't see a valve) but the video lacked so much information I could only concur that 2000fps seems quite unlikely. I figured the recoil could be some-what hidden in a gun with a heavy enough frame and supports like in the video but the lack of recoil altogether is highly suspicious.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 05, 2012 4:53 am

MrCrowley wrote:I figured the recoil could be some-what hidden in a gun with a heavy enough frame and supports like in the video but the lack of recoil altogether is highly suspicious.


We're talking over 6000 ft/lbs muzzle energy for a golf ball at twice the speed of sound, even a heavy frame would at least flinch visibly, particularly given the height of the barrel centreline from the ground as well as the fact that in the video it's fired at a relatively horizontal angle.
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Unread postAuthor: MrCrowley » Mon Mar 05, 2012 5:00 am

Exactly, I can hide the horizontal kick on my cannon due to the cross support but it'd be near impossible for me to physically stop the cannon from jerking up. It's hard to say without more information but it seems possible the cannon in the video may only be getting around 700fps. 500fps is enough to shoot a golf ball ~450m, add a bit more oomph and some helpful winds and you can probably get your half mile.
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Unread postAuthor: mobile chernobyl » Mon Mar 05, 2012 8:52 am

Hmmm... I'll first off have to say that that video is one of my favorites! Not so much for the gun (although it is a cool platform for plinking) but for the amazing "shooting range" he has.

Next - no way is he shooting 2000fps. I'd wager that even 1000fps is a far stretch. now, not many of us on here if any have made "Detguns" where the purpose is to ignite a known detonating mixture of oxygen and a fuel (acetylene being a potent one) so there is not much "proof" that this mixture has supersonic powers.

A simple GasEQ run yields less than satisfactory results at stoich - and a potential for about 350psi under GasEQ's mysterious "ideal" conditions (rich fuel mixtures). Here's two screen grabs:

Image
Stoichiometric^
Image
Fuel Rich^

Also about the recoil - JSR I would have to agree. As a shameless plug - and an example of a turret mounted gun that CAN accelerate a golfball in the 1700fps range - there is noticeable recoil even after accumulating a total gun weight of over 60 pounds.
[youtube]http://www.youtube.com/watch?v=-CBpkZquKbI[/youtube]

At the end of the day - I think under ideal stoich conditions he's seeing between 500-700 fps at most. More likely he's seeing right around 500fps as a high number.

But someone should really build one of these "oxy-fuel" cannons and shoot it through a chrono so we can build a better model off of the combustion/detonation kinetics... cheap summer segway project for myself perhaps :roll:
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Unread postAuthor: Daviator » Mon Mar 05, 2012 1:47 pm

well thats unfortunate. i was hoping that this would achieve supersonic speeds,and since its simple to build wouldnt require so much time as some of they hybrids look like they would.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 05, 2012 4:02 pm

Daviator wrote:well thats unfortunate. i was hoping that this would achieve supersonic speeds,and since its simple to build wouldnt require so much time as some of they hybrids look like they would.


A fuel/oxygen hybrid could well go supersonic with the right parameters, so if you're comfortable with and competent enough to make something that will take the pressure go for it.
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