New member, first cannon.

[dtdynamics]

After browsing the site for a while and realising just how simply these things can be made i decided id waste some money and try build one for shits and giggles

criteria was initially to be cheap, simple and able to shoot 6mm BB's (plastic and ball bearings) with at least more force than an airsoft. (1 joule limits in my country)
using 160psi as its the highest thats easily obtained with pumps that i can find cheap.
also i wanted to spend less than €100 in total in making this.

Bitta research into the different items needed I compiled a list and then set about getting an idea of how id lay it out using solidworks.

The main parts being 15mm copper pipe 300mm in length for the chamber.
1/2" "European style" QEV
usual 1/2" bst plumbing fittings
1/4" bst blowgun
650mm 6.03mm airsoft barrel

I tried out GGDT and got the following although having never used it before I probably went wrong somewhere.
0.25g 6mm airsoft it reckons velocity of about 220 m/s (6.2joule)
and 150 m/s (10joule) for 6mm steel ball bearings weighting approx 0.89g.

I then decided I didn't really want such a long barrel so I will probably go for a 400mm barrel which brings the above figures down to 188 m/s (4.4joule) and 125 m/s (6.9 joule) respectively.
big hit in performance for a shortening of barrel but I was happy enough with the estimated power.

As of this post I have all the parts minus the barrel and only need to machine the blanking endcap on the tee joint to fit the schrader valve and I can begin low pressure testing with a much smaller airsoft barrel I have lying about.
picture included with plastic barrel for mock up and I want to try mount a rail to mount a scope like shown.

[dtdynamics]

finally got a chance to finish the gun and acquired a stainless 500mm barrel 8mm OD and 6mm ID.
I had hoped to use this barrel with airsoft bb's and 6mm steel ball bearings but the ID is actually slightly undersize at about 5.9mm so they wont work but i can get 5.5mm bearings instead and also .22 ammo.

I have only tried it with this barrel under 60psi so far till I sort out the breech loading and few other bits.

i found a pretty good fit projectile which is the rear part of a dart! its a slightly loose fit in the barrel but i used it for the test shots.

i took two shots at a DIY chrony one at 30 psi and the other at 60psi.
projectile weighs 1.3 grams.
30psi = 29m/s (0.55 Joule)
60psi= 63m/s (2.58 Joule)
pinch of salt on the above figures but they are pretty close
with the pump I bought i can manage 200psi but any higher is nearly impossible to pump so it would be interesting to see if the velocity scales up at high pressure.

[jackssmirkingrevenge]

Nicely done for a first project (and nice SW rendering too ). If power is what you're after you should really consider higher pressures, essential for small calibres.

A fridge compressor should be easy to come by cheaply and will happily take that chamber to 300-400 psi in little time.

You might also want to think about making your own high pressure pump, fairly simple if you follow this excellent tutorial: http://www.spudfiles.com/forums/easy-st ... 13277.html

You can also boost performance by reducing pilot volume, here's a suggestion from this thread. Basically you would thread the blowgun directly to the QEV and fit the schrader to the other end, with its core removed so the blowgun valve becomes the fill and pilot valve.

Here's a compromise solution, fit a schrader valve to the blowgun and remove the core. This way, you can fill through the pilot (provided the blowgun is held open) and when you pilot, the flow isn't really restricted. You can improve it further by drilling out the schrader to 4.5mm

Postal cat silencer optional

[dtdynamics]

Thanks for the idea's! il look into them, for now I can see me having some fun with the 200psi I can manage

also on the pilot volume I was thinking would another solution be to fill the tee joint i have on with epoxy or silicone and then just drill really thin passages to keep the volume very small, any thoughts?

also for anyone interested I had set a budget of under €100 and finally tally is €90 which includes the €20 high pressure bike pump.

[dtdynamics]

Managed to add breech loading to it and found some very good ammo to use with it M6 threaded rod is a perfect fit!

I know i added a bit of dead space with the breech loader but it still shoots very well! at 60 psi an 8mm piece of M6 rod went cleanly through a can and the 6mm thick fiberboard that was behind it!

I also added a basic barrel support as ya might have noticed