SpudFiles

Hello.
Im about to start my new project which is a 6mm coaxial. I know the power wont be really impressive, its just to introduce myself to coaxials, as i have never build one before.
My plan is 100cm of ½" galvanized pipe chamber with a 140cm 8mm copper pipe barrel. I will probably be running it at around 20bar, maybe more. My main ammo would be .89g steel bb's.
My question is, what velocity would i be looking at with a 0.12g bb? GGDT predicts 568m/s which i consider a bit next to reality. 012g bb's are a cheap alternative to the steel ones, so i was just wondering if they were at all useable as ammo.
Thanks in advance

you should be getting 800-1000 fps as a guess because anything more is unrealistic as it is approaching the speed of sound

Alasdair.

I think you might be wrong about the power.That will easily outdo the average off the shelf airgun.

GGDT won't be too far off, maybe the estimate is even a little low...

with that much chamber Id say 1000fps-1100fps, just a little below the sound barrier.
if you uped the pressure to say 500psi, then you actually may break the sound barrier

^^^ he would need to heat the air.....

I disagree
as long as it was at a moderatly high temp(70degrees F and above)I think he would have a fairly good chance at it
of course it will ba a lot hader to do with a piston valve than a burst disk but Id say its possible.

hmm whats 70 degrees in celcius... (i'm a brit)..... ahhh 21 degrees C..... thats not that hot, and the fact that the speed of sound increases with temperature.....

Alasdair.

lol I thought that 70 degrees C is 70 degrees C....

I hope one day world would use one set of (metric ) units

To be honest im not that known in the area of supersonic spudding, but it could be funny to make a supersonic gun. I know that supersonic is possible with compressed air(commercially available guns) but i also know that noone i have heard of yet has achieved it with a pneumatic spudgun, so its deifnately not easy.
Brianthebrain can you tell me why you think GGDT is underestimating the power? sounds interesting 8)

Well..that was to emphesise GGDT did not predict "next to reality"

It is more or less correct most of the time as far as I know.

I'm just not sure you entered all the right dimensions.Because my guts tell me you are gonna get about mach 0.8 of the speed of sound.
But what do I know?

You probably know more than me on this area
i guess that i will just have to try and make this and see how it goes
thanks everybody

With those specifications you'll be doing high subsonic velocities with lightweight projectiles, but I doubt you'll go supersonic. However with heavier projectiles as to performance I'd expect you'd get in the 15-30 ft/lbs region, it will make a decent sniper rifle

jackssmirkingrevenge wrote:With those specifications you'll be doing high subsonic velocities with lightweight projectiles, but I doubt you'll go supersonic. However with heavier projectiles as to performance I'd expect you'd get in the 15-30 ft/lbs region, it will make a decent sniper rifle

Any ideas on how high pressure would have to be to go supersonic?
And yeah, my idea was to make something a bit more accurate with a little less power than usually, so i think this will suit my needs wouldnt exactly call it a sniper rifle, but lets not start that discussion

There's only way to find out, keep pumping with my 6mm burst disk at around 28 bar the best i got was just over 1100 feet per second.

What are you using as a piston and how will it be piloted?

I wouldn't say 0.12 gram BBs are very useful ammo, they do fly fast but lost velocity very quickly, both as they travel in the air and through a target.

Look at the difference in penetration between a 0.25g BB and a 0.12g BB from the burst disk launcher.

jackssmirkingrevenge wrote:There's only way to find out, keep pumping with my 6mm burst disk at around 28 bar the best i got was just over 1100 feet per second.

What are you using as a piston and how will it be piloted?

I wouldn't say 0.12 gram BBs are very useful ammo, they do fly fast but lost velocity very quickly, both as they travel in the air and through a target.

Look at the difference in penetration between a 0.25g BB and a 0.12g BB from the burst disk launcher.

Well, pressure is not a problem as i have a fridge compressor, my concern is how much pressure i dare putting into the gun. i honestly have no clue on how high ½" galvanized fittings are rated.
I have yet to decide on a piston, so im open for suggestions my thought on piloting was a 3/8" qev (crossed fingers hoping to get it on ebay) and a blowgun for easy triggering.
I wasnt planning on using 0.12gram bbs as main ammo, just as a cheap alternative. Looking at your "test results" i have great expectations for the 0.89g steel bbs