I has semiauto ;-)

[psycix]

Marbles are cheap and nice ammo on one hand.
On the other hand, they suck.

I have the same problem, but my barrel is 16.1 or so, and about 1/2 to 2/3 of em fit.
I'm going to buy some stainless steel ball bearings.... 16.000 mm size
Or else Im just gonna make some steel cylinders on the lathe.

[Technician1002]

but still, the fact that you can see the marbles in flight suggests that the velocity is fairly low,

This is a misconception. Many digital video cameras have high shutter speeds, so they can catch a frame with the projectile. The question is is it slow enough to be in a series of frames. Are any shots fast enough that it made the distance between frames and is only seen after impact. Time for a little slow frame by frame examination to find out.

[jackssmirkingrevenge]

This is a misconception. Many digital video cameras have high shutter speeds, so they can catch a frame with the projectile. The question is is it slow enough to be in a series of frames. Are any shots fast enough that it made the distance between frames and is only seen after impact. Time for a little slow frame by frame examination to find out.

Be that as it may, you can see the marbles flying by in the "low velocity" video, but not in the "high velocity" one

[POLAND_SPUD]

@ JSR&tech
JSR it might be just a matter of scale... normally you shoot small bore projectiles or at relatively short ranges...

I realize that velocity was rather low (my guesstimate - 100 m/s but I am not really good at it) but they were to be visible on this vid...

also notice that the distance here is about 15 meters
let's model flight time in chairgun:
it takes 0.1 second for a marble to travel 15 meters at 155m/s...
(that's 3 frames)

at 200m/s it covers 19 meters in 0.1 sec.
at 100m/s it covers 15 meters in 0.16 sec. (that's 5 frames)

what is more, marbles can be (surprisingly) easy to notice as they reflect light very good... this actually can be useful because they make pretty good tracer rounds even at high velocity
(that's actually something worth trying - you'd be surprised how fu## ## their flight path is)

EDIT
a couple of minutes after writing this post I found a measuring tape in my basement... so I wanted to check the exact distance...

it turned out it's a little bit further than 19 meters from where I fire to the place where I put my targets...

I made a few collateral damage pics (aka DYI backstop syndrome) as well...
now you know why my mother doesn't approve of my hobby...

[POLAND_SPUD]

I've decided that it might be a better idea to switch to 8,731mm / 11/32” ball bearings ( ~2.6g) and 9mm barrel...
I changed my mind as it's easier to find parts in that calibre and I oculd acheive higher muzzle velocity

on that version I am going to concentrate on making the gun compact & ergonomic... I might use 88g. co2 to make it fully self contained... so it will be sort of like m4 of spudgunning



I might one day build a high power version using larger bore (possibly 0.5")... on that gun I am going to concetrate on power and accuracy while sacrificing mag capacity

any ideas or comments about this?? would 8.731mm BB will fit tightly in 9mm barrel ?? also do you htink I could find some ready-made lead ammo for 9mm barrel?



ohh btw it seems that 'FILE0069.JPG' in my previous post clearly proves that ammo travelling at high speed makes smaller holes

[jackssmirkingrevenge]

I've decided that it might be a better idea to switch to 8,731mm / 11/32” ball bearings ( ~2.6g) and 9mm barrel...
I changed my mind as it's easier to find parts in that calibre and I oculd acheive higher muzzle velocity

Going down a similar route myself pending some deliveries.

any ideas or comments about this?? would 8.731mm BB will fit tightly in 9mm barrel ?? also do you htink I could find some ready-made lead ammo for 9mm barrel?

You can find steel BBs sold as 3/8" - 9mm slingshot ammunition, surely these would be a better fit?

ohh btw it seems that 'FILE0069.JPG' in my previous post clearly proves that ammo travelling at high speed makes smaller holes

A high speed projectile does not give the target time to react, and in a solid medium will leave a projectile sized hole. A slower projectile gives time for stress to be placed at areas further away from the point of impact resulting in a bigger, fractured hole in certain media such as plastic in this case.

And yes, that's pretty much what pots in our garden look like

[POLAND_SPUD]

3/8" is 9,525mm (3.55 g)... that won't fit 9mm ID barrel to well... that's ammo I wanted to use earlier

8.731mm in 9mm barrel - that's 0.289mm gap... isn't that slightly too big ??


I've already found both the ammo (already ordered) and the hydraulic tube (12 X 1.5mm)


also what about 88g co2 cartridges ?? any ideas how to connected them to standard NPT fittings...? AFAIK they have 15mm X 1.5 threads

[jackssmirkingrevenge]

3/8" is 9,525mm (3.55 g)... that won't fit 9mm ID barrel to well... that's ammo I wanted to use earlier

Unless you're the sort of lucky bastard who happens to stumble upon 3/8" I/D brass tubing in Europe

8.731mm in 9mm barrel - that's 0.289mm gap... isn't that slightly too big ??

My oft quoted test for barrel tightness showed that for a 4.5mm lead BB, the difference in power between a 4.5mm I/D barrel and a 5.0mm I/D barrel was a dramatic 33% increase for the tighter barrel. In your case however I doubt it will make much of a difference.

also what about 88g co2 cartridges ?? any ideas how to connected them to standard NPT fittings...? AFAIK they have 15mm X 1.5 threads

Discussed it here

[spudamine]

also what about 88g co2 cartridges ?? any ideas how to connected them to standard NPT fittings...? AFAIK they have 15mm X 1.5 threads

it's a 16mm x 1.5 I believe, nearly there

I bought a tap and made a manifold, the thread doesn't form a seal just pushes the neck down on an O-ring. It was initially designed to be able to pierce a full cylinder but I chickened out for now and use it with air at 600psi. The modification should be simple to make though just tap a hole in the back for a sharpened bolt.

[POLAND_SPUD]

uhmmm engeneering tool box suggest that 3/8" NPT almost fits 15 X 1.5mm ...
lol life would be so much easier if there were metric units only...

as far as CO2 and high pressure is concerned I think that 3/8" and 1/2" malleable can handle it but just to be sure I plan to either use a good reg (if I can find one that regs down to 400 - 500 psi)

or

build a home-made sort-of-reg... I hope that I could increase crack pressure of tire valve to 150-200 psi by replacing the spring with a stronger one... in this way I could use one or two of them to bring down pressure to 450 - 600 psi or so...


hey BTW that looks like a pretty nice gun... how come it hasn't been posted yet ??

[spudamine]

hey BTW that looks like a pretty nice gun... how come it hasn't been posted yet ??

As of yet unfinished, It will actually work on a similar basis to yours, there is a piston in the brass section of chamber above the slide valve which connects to a moving barrel through the rest of the chamber and loads a round whenever the chamber is pressurised. The two 88g cylinders are a reserve chamber which fill the main chamber when the slide valve is moved. I tried a regulator as well but the flow was crap after a few shots when everything cooled down. I'm to scared to try unregged yet, If i ever get it working well I might invest in a remote paintball CO2 setup, keeping the two 88g tanks as a buffer chamber. For now I just use my pump.
What's taking so long is the magazine and breech, saboted darts are a bit tricky to feed automatically...

[jackssmirkingrevenge]

What's taking so long is the magazine and breech, saboted darts are a bit tricky to feed automatically...

Unless you put them in a cartridge

[spudamine]

I've looked at that design before and I like it, but I think efficiency suffers a bit. My design will be tricky to build but there should be no loss of efficiency over a standard breech loader.
I think the only way to really go with cartridges is your hybrid design. If I ever get the time I will definately be having a crack at that

[POLAND_SPUD]

to tell you the truth I am scared as hell when I use 550 psi so yeah unregged CO2 does seem quite dangerous to me too...

have you considered changing the design to the one I used on the newest version ?? I am talking about the solid bolt and the T that joins all the basic parts ( the air cylinder, QEV and barrel)?

normally it's better to have no bends between the valve and the barrel but then you have to use a blow-through bolt... it improves ergonomics a lot and shortens the gun

Unless you put them in a cartridge

notice that it uses a similar design - ammo is loaded from the back

[jackssmirkingrevenge]

I've looked at that design before and I like it, but I think efficiency suffers a bit.

Precisely the reason why I abandoned it, mechanical interest projects are cool but MOAR POWER! is also a requirement

I think the only way to really go with cartridges is your hybrid design. If I ever get the time I will definately be having a crack at that

That would be something I would watch with interest, perhaps it should be suggested as a community project