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combustion rifle ?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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combustion rifle ?

Unread postAuthor: goa » Sun Oct 30, 2011 4:42 pm

hi , i've been lurking the forum for a few days now.
i was planning to make a combustion rifle . but i don't know
how am i going to make a chamber. since the barrel would be much smaller in diameter if im not mistaken the pressure inside chamber is going to be much higher than in those of cannons. so i don't thrust pressure rated pvc much. i was thinking would 1kg fire extinguisher chamber be sufficient at
those pressures . but if i take fire extinguisher i don't know how am i going to put a fan inside. so does anyone have a solution. maybe pressure rated pvc would be enough...

your thoughts ?
oh and i was planning to use 16mm marbles as ammo.

tnx
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Unread postAuthor: Zeus » Sun Oct 30, 2011 4:56 pm

A standard combustion fueled with propane or butane will <b>never</b> exceed the ratings for pressure rated PVC. Assuming this will be a spray and pray, I doubt the presssure will exceed 90PSI.

I don't trust PVC in pneumatics, if you drop the launcher while it's pressurized, there will be PVC shards everywhere. In a combustion that isn't the case, they are far safer.

And marbles are a good fit in 1/2 (15mm) PVC, the pipe isn't actually 1/2 inch, that's a nominal size.
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Unread postAuthor: goa » Sun Oct 30, 2011 5:06 pm

oh . so speaking about power , pneumatic would be more powerful ?
i would take some marbles with me to test fit them in pipe anyway . thanks for warning anyway. :wink:
i was planing on putting a ball valve at the back and inject butane with that plastic thing people get shots with, ( i do not know what is that called in english) so i think that would make a more powerful mix.
what would you say maximum possible pressure would be then ?
taking in consideration exit pipe diameter .
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Unread postAuthor: Zeus » Sun Oct 30, 2011 5:24 pm

If you use PVC, then you won't exceed 100PSI with air, so the power will be fairly close, I would recommend you use a sprinkler valve, that will be more reliable and simple to make.

Injectng butane with a syringe is good, just make sure that you can vent the chamber of exhaust gases. A good thread about syringe fuel metering is here.
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Unread postAuthor: goa » Sun Oct 30, 2011 6:00 pm

i would prefer a combustion. if you say pressure rated pvc is fine i believe you and think it is going to be fine.
i don't agree on simplicity. combustion is simpler if you ask me.
where would i get an electronic sprinkler valve in croatia ?
nowhere . and if i find it it would be around $100.
for a combustion i only have to make a chamber , and mount a piezoelectric
sparker and a fan. mount barrel to one end and ball valve on other.

in this case i would prefer for this rifle to look nice. i don't plan on making something deadly but it would be nice to shoot as good as it would look.
so maybe ill make a wooden stock .
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Unread postAuthor: saefroch » Sun Oct 30, 2011 6:09 pm

Why would you look specifically for an electronic sprinkler valve? A mechanically piloted one will probably be slightly better.
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Unread postAuthor: Crna Legija » Sun Oct 30, 2011 8:03 pm

goa wrote:croatia ?


Ja ne znam gdje bi mogao naći jednom biti ja sam također iz Hrvatske, ali ja živim u Australiji.

provjerite eBay za njih, ako ne ih pronaći ili ako ne mogu koristiti eBay, možete koristiti bljeskalicu za kameru da bi jedan. kao što je ovaj
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Unread postAuthor: goa » Sun Oct 30, 2011 8:45 pm

thanks crna legija but i think its a lot simpler to make a combustion rifle.
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Unread postAuthor: jackssmirkingrevenge » Sun Oct 30, 2011 11:57 pm

As others have stated you'll be fine with pressure rated PVC. If you want power and consistency, meter your fuel well. Not sure what sort of plastic electrical conduit you have in Croatia but if it's of the 20mm OD type, ID is usually around 16.5mm for an ideal barrel.
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