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12 bore HPA coaxial

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: blind909 » Sun Jul 11, 2010 3:14 pm

That looks like a very unusual, but totally awsome way of making a supressor JSR.
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 11, 2010 5:53 pm

Never made one like this before but you certainly gain a lot of volume by having the barrel out of the main tube. In this case, the main tube alone has a volume of around 13 cubic inches, over 25 times the volume of the chamber. I've also split it into two chambers as you can see from the internal diagram, which should make it even more effective.

I might also have to make an attachment for the pilot as it will likely be louder than the muzzle blast itself, a simple clip-on expansion chamber should suffice.
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Attachments
12boremockup.JPG
Quick mock-up of what the final configuration should look like. Still needs a lot of finishing but the suppressor unit is essentially done. For the trigger, it will likely be a rod leading up to the ball valve.
12boresuppressorint.GIF
Actual internal configuration of the suppressor
12boresuppressorint.GIF (3.16 KiB) Viewed 860 times
12boreplannedconfig.gif
planned trigger/pistol grip configuration
12boreplannedconfig.gif (4.4 KiB) Viewed 818 times
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Unread postAuthor: chinnerz » Mon Jul 12, 2010 1:28 am

Haha! That looks outrageous!! A bit of cleaning and that is going to look AWESOME!
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 12, 2010 2:28 am

I'm normally reluctant to finish off my launchers aesthetically and ergonomically, due to the non-servicable nature of epoxy construction should something go wrong inside I will have to throw the whole thing away so I don't bother.

In this case, the only moving part is the piston, which doesn't need lubrication, plus the seal is 1/2" thick neoprene which is unlikely to wear out throughout the life of the launcher, and the pilot/fill valve setup is removable, so I'm more confident with making a completed launcher. Always wanted a riot gun lookalike in my armoury :) At 18" barrel length it's not quite at "sawn-off", but I'd rather gain a couple of inches of barrel length if it means more power and less noise.

I'll take it to 800 psi tonight and see how it performs. By my reckoning suppressor pressures shouldn't exceed 10 psi so hopefully nothing will blow out :) Having the temperatures at Scorchio! might be annoying but it speeds up epoxy curing times remarkably, it's almost fully cured after a mere 6 hours :D
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Unread postAuthor: jakethebeast » Mon Jul 12, 2010 4:49 am

waiting for the info of the 800psi shots, lets just hope that you wouldnt kill yourself :roll:
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 12, 2010 5:02 am

I'm confident the chamber will hold that pressure so no worries there, as to ricochets... well, I've learnt my lesson :)

Given that the suppressor volume is greater than the expanded volume of HPA in the chamber at atmospheric pressure, there is a concern that a vacuum will be created in the barrel before the projectile exits the muzzle, thereby slowing it down. It should be noted however that the ports through which air can flow into the suppressor chambers have an area 6 times smaller than the area of the barrel. As there are three of them in total air can only fill the suppressor at a maximum rate around half of the rate through the barrel, so this eventuality should be avoided.
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 12, 2010 11:31 am

I've just done some testing, here are some velocity and muzzle energy results using a 30 gram CO<sub>2</sub> capsule:

barrel without suppressor at 100 psi: 40.7 fps / 1.7 ft/lbs

barrel without suppressor at 500 psi: 190.5 fps / 37.3 ft/lbs

barrel with suppressor at 500 psi: 180.9 fps / 33.6 ft/lbs

barrel with suppressor at 800 psi: 250.8 fps / 64.6 ft/lbs

As you can see, the suppressor cut 10 fps from the muzzle velocity at 500 psi, doesn't sound like much but for a relatively heavy projectile it cuts almost 4 ft/lbs from the muzzle energy, that difference is more than what most CO<sub>2</sub> 0.177" pistols will manage.

The energy increase at 800 psi is fantastic, and while the suppressor made a difference at 500 psi - more of a "whoosh" than a sharp crack - at 800 psi, *quite* loud, but I can't tell the difference because I hadn't fired it at 800 without the suppressor.

I decided to give the UPS steel case another go, but as I was filling the chamber sprang a leak. I'm guessing the pressure stretched out the copper tube a little. I tried it subsequently at 150 psi and there were no apaprent leaks, but it leaked at 500. I've added some reinforcing epoxy, and put the innards under some vacuum with a large syringe to attempt to such in some epoxy into any hairline leaks.

Since I had the target and camera set up I took the shot anyway, no idea what the pressure was but it didn't quite punch through - still, made a bigger hole.

[youtube]http://www.youtube.com/watch?v=BJdSTxmjY54[/youtube]
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Unread postAuthor: Gun Freak » Mon Jul 12, 2010 11:36 am

Why didn't you try the suppressor with a 100 psi shot to compare?
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 12, 2010 11:40 am

Didn't seem to be be worth it, considering the pathetic energy at that pressure I wouldn't really be using it at 100 psi.
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Unread postAuthor: Gun Freak » Mon Jul 12, 2010 11:53 am

Ok but why did you choose such a small chamber in the first place? A bigger chamber would make a HUGE difference!
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 12, 2010 12:03 pm

In a word - noise

I live in an urban area and don't have the luxury of wide secluded expanses over which to shoot, so anything that sounds like a gun shot is simply out of the question. I would have loved to make this with a 72" barrel and 1:1 C:B ratio, but until I move to the American midwest that can't really happen :roll:
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Unread postAuthor: dewey-1 » Mon Jul 12, 2010 12:13 pm

jackssmirkingrevenge wrote:In a word - noise

but until I move to the American midwest that can't really happen :roll:


There goes the neighborhood to hell! :D

I thought Hawaii was your destination? As in USGF location?
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Unread postAuthor: POLAND_SPUD » Mon Jul 12, 2010 12:14 pm

ok I am gonna say it one more time -> I wants valveless fullauto
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Unread postAuthor: Gun Freak » Mon Jul 12, 2010 12:22 pm

@Poland, bbmg's are valveless and full auto :tongue3:
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 12, 2010 1:09 pm

dewey-1 wrote:I thought Hawaii was your destination? As in USGF location?


I'd go there for the machine shop, but somehow Hawaii doesn't conjure up images of golden fields stretching out to the horizon :roll: :D

SZALONY_MASZYNOWY wrote:ok I am gonna say it one more time -> I wants valveless fullauto


I wants valveless select fire, in a more sensible calibre - 'cause there's no way I'm going full auto with a 0.75" HPA launcher :shock:

I was thinking of maybe giving this another go, with a more carefully built spring loaded magazine and ball valve trigger. That or 0.22" with lead pellets, but spherical projectiles are so much easier to load reliably.

Ridiculously unsafe air"soft" is also an option, GGDT predicts that with 800 psi, a mere 0.2 cubic inches of chamber volume and a 24" barrel, a valveless airsoft launcher will be pushing a 0.25g BB beyond 1,000 fps and 10 ft/lbs :D
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