SpudFiles

this probably wouldnt work but is there any way to put a burst disk inside of a coaxial?

Helium or hydrogen.
Pump that in and the barrier is broken.

Sure guys, but that's hardly playing fair now is it.

This experiment is based partly on the fact that I believe Jack never HAD 400psi air in the chamber.

I don't believe a burst disk is necessary either.

By keeping the chamber "large-ish" diameter wise, the flow in the chamber should (I think) remain sub-sonic. Which will slow or eliminate the formation of shock waves in the chamber, causing flow restriction.

This high speed but subsonic flow, has to accelerate at the barrel.

Hope that makes sense.

Ultimately, this should be a reproducible experiment.



Edit: Pellet test results. 14.3 grain benji domes with the skirts swaged up, @ 400psi the one shot that registered was doing 739.5fps at the 5 foot distance.

I was hoping for more. On the plus side, they did penetrate a bit more than 1" into the backstop/book.


Tear down and modification will be the next step.

Edit: Ok, I brutalized the barrel taking it apart. It is now 34.5" in length.
I made a nozzle for the barrel inlet from brass, it has a 12 degree taper, and is .340" at the inlet.

I soldered everything back together at lunch, and fired a couple shots over the chrony.

I got a reading of 1045fps.(airsoft bb)

Not an overly impressive result for the modification.

A second shot was attempted, but the piston wouldn't seal. Tear down revealed that the teflon puck had been pulled out of the piston. It was pressed back in place, the launcher re-assembled, and another shot was fired.

This one came in at 1049fps. Not bad for deviation, but still not an improvement. The teflon puck came free again as well.

I popped the piston in the lathe, drilled a pilot hole and counter sink for a screw, and secured the f'ing puck in place.

Testing to resume tomorrow.

WOW, I never knew I was supposed to be standing back from the crony. I hope my results aren't way off.

Correct me if I'm wrong but I thought unheated air powered guns could not exceed the speed of sound because the expanding air couldn't break it's own shock wave. But the other day I saw a pellet rifle and Cabela's that said "1200 fps".

sweet gun btw

air powered guns can reach supersonic. look at the airforce condor airgun.

The condor uses the brute force available from 3000psi. It's not your average spuddy.

Springer air rifles shock heat the air, hot air allows higher velocities. Gamo has a springer with a claimed mv of 1600fps with extremely light pellets.

My understanding was that the highest, theoretically possible velocity with room temp air was around 1600fps.

It would seem that even if my bb's aren't supersonic yet, the muzzle blast is. I can't explain the 1200+fps readings any other way.

That would seem to indicate that air CAN travel faster than mach 1. While not conclusive proof, it does give me hope that a mach 1 bb is at least a possibility.

In any event, I'll be plunking away at this until either I get a reproducible reading of mach 1, or my head gets sore from beating it on this wall.

By keeping the chamber "large-ish" diameter wise, the flow in the chamber should (I think) remain sub-sonic. Which will slow or eliminate the formation of shock waves in the chamber, causing flow restriction.

This high speed but subsonic flow, has to accelerate at the barrel.

Hope that makes sense.

hmm so if i want decent performance from my BB plinker under construction from spares, i need to pic up some 22mm copper instead of 15mm copper to house my 0.8cm barrel in....

Don Gippeto wrote:Gamo has a springer with a claimed mv of 1600fps with extremely light pellets.

Claimed. Most independent tests don't actually put it that high. To be frank, most manufacturer claimed air rifle velocities are overgenerous.

My understanding was that the highest, theoretically possible velocity with room temp air was around 1600fps.

In an evacuated, completely frictionless and flawless barrel (not to mention a very long one) with a near infinite C:B ratio. Real world issues prevent the theoretical ideal coming into play.

It would seem that even if my bb's aren't supersonic yet, the muzzle blast is. I can't explain the 1200+fps readings any other way.

That depends on whether the chrony reads the head or tail of the projectile.

If it reads the tail end, and the muzzle blast is blocking the near sensor for a few fractions of a second longer than the projectile actually is, but isn't registering on the far sensor, then that would appear to the chrony that the projectile had passed the sensors in less time than it actually had, making it appear faster.

However, I don't know what most chronys read, as I'm no electronics expert. But from a ballistics viewpoint, there are advantages to reading either.

How did you secure the barrel to the chamber anyways? Epoxy cast?

Ali, ggdt predicts the same velocities for both diameters if the chamber volume remains the same.

Call this a theory, or half remembered (forgotten?) physics then.

Ragnarok; Yes and Yes. This is why I said "claimed" and "theoretical".

I've set the chrony up in the hallway again (with the light kit), and have been doing some testing with this thing. (Ear plugs are great!)

According to the manual, the chrony detects a momentary change in light intensity.

Out of curiosity, I dry fired it ~6" from the chrony to discern the effect of the muzzle blast alone on the sensor.

There was no reading, and no error. (If the first sensor had picked up the muzzle blast, but not the second sensor, I would have gotten an error.)

Makes me wonder.

Sticky, I turned a brass piece on the lathe, and it's all soldered together.

Wow I guess I need to get one of those lathe gadgets. Maybe you should try yourself at one of these just for the hell of it you do have those exstinquishers right? http://www.ora8i.rivington-riflemen.org ... idges.html

Interesting, no doubt about it.

But the cost of the tap would exceed the amount I spend on cartridges for a year.( there are a 1077 and a 357-8 in the cabinet)

Following Marks build up of his 1377, got me "fired up", and I modded my old 1322.

I pretty much use it exclusively now.

i'm thinking that we need a test to compare how chamber diameter affects velocity in coaxials... to see if your theory is right... i would do it.. but i don't have a chrony

p.s. thats a cool air rifle (and maybe mark should have called his the 1337 )

Backpacker airgun cool.http://www.canadiantire.ca/browse/produ ... earch=true You ever use it like a pistol? You must not buy too many cartidges then, exspencive for such a small ammount. Wouldn't your work have the taps? EDIT: Btw This is the pistol I am looking at getting walther ppk/s airpistol http://www.z-shops.eu/images/Walther%20 ... dvbgfb.jpg

Subtlety at its finest. Akin to a brick up the side of ones head.

I will agree that the testing should be done, and I'll add it to my list.

And thanks, it's a fun project, and one of my more practical ones. Still a few pieces to change out/make, but it's getting there.