SpudFiles

best err on the side of caution

You can buy an F1 chrony for less than a hundred quid, much less second hand if you check out the "for sale" section of UK shooting forums. You might also want to consider the Combro, cheap, effective, portable and with a superb aftersales service if you accidentally shoot it (and many people do...) - the problem with the latter is that you´re limited to projectiles of 10mm diameter or less, and you can only measure velocity at the muzzle.

Well since I've got a bore of 14mm that last one's not going to be very useful

I might get a meter later

Thanks Hotwired!! You have some of the best guns I have ever seen. Could you give me a link to that post where you won the competition? I want to see your other gun.

The forum is http://www.uksgc.co.uk/

You don't really want to find my other cannon though, theres reasons why I never bothered posting it here

Hey I'm not purposely trying to bring back an old topic here but I'm a bit confused about your C:B ratio of 2.62:1.

Details:

Chamber = 60cm of 22mm copper pipe
Barrel = 100cm of 15mm copper pipe
C:B ratio = 2.62:1

I calculated your chamber to be 228.1 cm/cu and your barrel to be 176.7 cm/cu. 228.1 is not 2.62 times bigger than 176.7, I calculated your C:B ratio to be 1.29:1.

So ummm, how did you get a C:B ratio of 2.62:1? Were you also putting pressure into the equation? Or am i just fully wrong, I don't know cause I'm not that good at maths?

1.29:1 looks right, but i didnt do the math so i dont know. it just looks alot more down to earth than 2.62:1. i could be wrong just as you are...

I got the ratio of 1.36:1 if you include the 0.7mm wall thickness on the 15mm pipe and the 0.9mm wall thickness on the 22mm pipe.

aha, so I'm not wrong after all. So where's the hidden chamber on copper head prime?

Hmm.

I'm not actually sure where that came from now

Oh well, a quick check does show that the 2.6 one can't be right so I have no idea, just one of those mistakes

*edits original post*

Thanks

Hey, it doesnt really matter, considering having a ratio above 2:1 is pretty inefficient, especially in a small gun like this one. You should be glad your C:B ratio is closer to 1.3:1

And by the way, very beatiful cannon. This one is great because it focuses mostly on ergonomics and aesthetics; I have never been able to do this, for I always focus on power... I am sure this is powerful too! The perfect spudgun 8) ?

Hehe,

The ratio is terrible really, its probably best for about 100psi but I crank it up to 240psi and you can really hear the inefficiency in the firing blast.

Thats the reason why I'm able to get ~5 good powered and vastly quieter shots out of its chamber if I rig it to fire as a (not-really-a) semi-auto.

You can blame that all on the aesthetics and ergonomics

If I gave it the 10cm chamber it actually needs to fire quietly but still with about 90% of the power it would have looked much worse and been less comfortable to use

did you have to mod the qev piston to use it to 240psi? as its only rated to 145psi? did you put a lacquer on it in the end?

The QEV is unmodded. That model is supposed to be able to handle 300psi if you believe the technobots website.

I haven't lacquered it or painted it.

I didn't paint it because firstly I didn't get the paint due to ordering issues then I decided that paint would mess up the barrel slides which need to be smooth and free of anything that might jam it.

The exposed copper oxidises and dulls over a month or so but five minutes work with some fine wire wool cleans it up nicely.

hey hotwired

I crank it up to 240psi and you can really hear the inefficiency in the firing blast.

how do you do that? just wondering, is it a dull sound or louder?

Well I've got two firing modes on it at the moment.

One dumps all the air in the chamber out in one go

The other can get several shots out of the chamber by losing about 40psi per shot.

A full powered shot makes a loud thump that echos off buildings and can crack a plank with the plastic slugs I'm now using. One of the multi-shot shots can crack the same plank but it's quiet enough to be fired in the garden without someone in the next garden even knowing about it.

I've also modelled it on GGDT with 240psi, by reducing the chamber to about 10cm from 60cm I lose a couple of fps but I've now got a chamber thats 1/6th the volume. Thats what I mean by inefficient.

An efficent barrel length for the chamber I've got at 240psi and emptying it in one go is about the length of a bus.