Hmm what to build...

[MrCrowley]

Okay so i've got a lot of free time in my Hardtech class and have nothing to do.

I have access to steel pipe and rod, about 10mm to 25mm and loads of square tubing of similar diameters.I also have access to quite a bit of nylon rod around 25mm.

I have a metal lathe, drill press and what not to make it all with.
So what should I build?

I'm stuck between a high pressure 6mm single shot BB gun or a semi-auto 6mm BB gun.

Pro's and Con's are obvious, signle shot powerful, but single shot.
Semi-auto, less power but more shooting.

So if anyone has any ideas they want to put into practice, I may be willing to do so. I'm bored and need something to do.

Any thoughts?

Oh and i'm willing to try anything from hammer valve to piston or what ever. Though i'd prefer to make something without a 'pilot', so generic pistons are out of the picture.

[FordGtMan]

How high of pressure are you thinking about? I would say semi, but if you have access to all that crap, make the first 6mm piston hybrid.

[MrCrowley]

300psi max probably. Unless those 12g CO2 canisters go higher.

[jackssmirkingrevenge]

I would try for semi-auto. My 6mm burst disk launcher is about as powerful as they come in small calibres (just over 20 ft/lbs if I recall correctly) and it got boring very quickly, but maybe that's because I own a 30 ft/lbs semi

How about something like this? Or you could always have a go at making a blow-forward breech/hammer valve hybrid.

If you want something relatively simple a blow-forward breech as reloading mechanism and blowgun as a valve should work well enough too, especially if you're using higher pressures.

[MrCrowley]

I'd prefer something more then a blowgun

The first link is a good design, same with the second. I'm just worried about the performance side of things. For the first one you need a strong spring to push the piston forward and open up the other piston, but it can't be too strong because it needs to be pushed back by the pressure.

I 'spose the same goes for the second.

I did have an idea floating around in my head where you have a piston that rides on a piece of pipe, the pipe leads to the chamber. Anyway the pressure pushes the piston forward on the piece of pipe and the piston seals the barrel. Air then leaks out of an equalization hole in the piston and fills up the 'secondary chamber'. If the secondary chamber was say 1" pipe, then the piston would be about 3/4" and ride on 15mm pipe.

So the secondary chamber would be the room between the piston and the 1" pipe, lenght wise it would extend from the piston to the barrel. So it could be any length.

Anyway, once this secondary chamber fills up, there would be more surface area pushing the piston back (it'd be made so it would) then forward, accompanied by a spring the piston would be pushed back and open up the barrel port.

I have no idea whether it would work or not, just an idea floating around. I guess it would cycle like full-auto. You could even put a rod on the front of the piston and use it to help with feeding in the barrel with a hopper.

This diagram isn't exactly the same idea, but is similar and may help you understand what the hell i'm talking about.

[jackssmirkingrevenge]

Interesting in theory and it would probably work in practice, I probably would avoid it though due to potential alignment issues and the need for perfectly sealed parts, I try to avoid using o-rings as much as possible - but that's a personal view.

There's also this idea to consider, "generic" piston to some extent but the bolt is wedded to the piston so it can perform both firing and reloading functions.

[MrCrowley]

Interesting in theory and it would probably work in practice, I probably would avoid it though due to potential alignment issues and the need for perfectly sealed parts, I try to avoid using o-rings as much as possible - but that's a personal view.

I wouldn't use the poppet type o-ringed sealing face as the diagram shows, alignment would be a b|tch. I'd try a generic piston sealing face and just have the barrel protrude into the chamber.

But yeah o-rings are quite difficult to perfect and sealing is always an issue. There's always cycling issues as well. I know you faced similar problems with one of your prototypes.

That's a nice design too. Again i'd like to try and stay away from pilots, though you could always have a hammer valve as a pilot valve which I know you have thrown the idea around.

[Carlman]

how about the first metal cannon with a SQUARE barrel? lol

oh and JSR i am looking to make a 6mm burst disk soon when i get my shock pump

[jackssmirkingrevenge]

how about the first metal cannon with a SQUARE barrel?

That would be sweet, or how about a rectangular barrel? Cutting sabots would be a doodle, plus you'd get futuristic railgun looks

I am looking to make a 6mm burst disk soon when i get my shock pump

Sweet, go for as long a barrel as you can manage and the biggest chamber volume you're willing to pump to high pressure, so you can enjoy it to the fullest

[MrCrowley]

I could always make a sqaure chamber

But I think I might settle for something like this:
http://www.spudfiles.com/forums/6mm-sem ... 10075.html

And instead of a compresser at 110psi, I would have a 300psi charged 15mm chamber, probably only get a few decent shots from it but I'm not too bothered now.

[Carlman]

remember a square shaped tube is not as good at holding pressure as a round one given materials.

[MrCrowley]

Yeah that's true. I wouldn't have made a square chamber anyway, unless I could've found the fittings.

I'm sure they still could hold a couple thousand PSI.