6mm coaxial

[hyldgaard]

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

[ALIHISGREAT]

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

Alasdair.

[Brian the brain]

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...

[bigbob12345]

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

[ALIHISGREAT]

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

[bigbob12345]

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.

[ALIHISGREAT]

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.

[POLAND_SPUD]

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

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

[hyldgaard]

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)

[Brian the brain]

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?

[hyldgaard]

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

[jackssmirkingrevenge]

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

[hyldgaard]

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

[jackssmirkingrevenge]

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.

[hyldgaard]

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