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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: frankrede » Sun Aug 10, 2008 12:24 pm

Why would it blow up from a longer barrel?
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Unread postAuthor: blind909 » Sun Aug 10, 2008 12:49 pm

He probably thinks it will blow up because there will be more pressure in the barrel, since the projectile will be in there for longer, so more pressure will build up, and he might have a DWV barrel.
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Unread postAuthor: starman » Sun Aug 10, 2008 1:15 pm

Don't worry about your gun blowing up because of a long barrel. Long barrels are desirable if you can manage the logistics of the large size.

Your only issue is the leverage strain on your sprinkler may cause it to fail.
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Unread postAuthor: Ragnarok » Sun Aug 10, 2008 2:00 pm

starman wrote:Long barrels are desirable if you can manage the logistics of the large size.

I personally got fed up of long barrels myself, although at one point I did angle for them.

A later version of Behemoth was fitted with a 150cm barrel and was 190cm long from front to rear - it was impractically long. It provided respectable power, but it wasn't worth the trouble. (Ironically, I'd made the decision to increase the barrel length from 100cm.)
HEAL cut that back to interchangeable 100 and 120cm barrels, with overall lengths of 124 and 144cm respectively. (Actually, have you guys ever seen the short version of HEAL?) That was much more practical.

Longer barrels do increase efficiency and power, but the practicality issues that arise are often not worth it in my own opinion.
It's especially a problem with PVC barrels, which aren't very rigid, and have a tendency to flop around - it's one of the things that limits the potential accuracy of a PVC launcher.
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Unread postAuthor: Floyd » Sun Aug 10, 2008 2:08 pm

starman wrote:Your only issue is the leverage strain on your sprinkler may cause it to fail.


Exactly what I meant.
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Unread postAuthor: nivekatoz » Sun Aug 10, 2008 2:58 pm

I noticed that most of your shots were with in 1 foot of the targrt..Since your barrel is rifled it should be able to hit the target from a far distance. You should try it.
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Unread postAuthor: Floyd » Sun Aug 10, 2008 3:06 pm

I think I will after I put a makeshift bipod on it and sleeve the barrel in some 1" pvc (it is a tad bit floppy just like Ragnorak said.) I'll do some long distance tests once it stops raining. (forecasted to go on the whole day........ :cry: )
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Unread postAuthor: nivekatoz » Sun Aug 10, 2008 6:01 pm

Cool. I would like to see the outcome..Should be good.
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Unread postAuthor: Ragnarok » Mon Aug 11, 2008 4:08 am

nivekatoz wrote:Since your barrel is rifled it should be able to hit the target from a far distance. You should try it.

The maximum effective range depends on all kinds of things. The relative rifling rate of the barrel compared to the projectile, how well the projectile can grip the rifling - not all rifling is equal.

An M-16 passes quality control if it can group 4" at 100 yards.
An AI AE rifle can shoot groups inside 1/4" at that same range.

Then again, it's even possible for polygonal rifling to best the results of conventional land-and-groove rifling. At the minute, there's fairly big talk in the air rifle world about a new variety of polygonally rifled barrel that's claimed to do big things.
Some of them too big - a problem I can see is that people are starting to expect the impossible from it. In fact, some of the actual claims made about it are beyond what is physically possible. It should improve accuracy, efficiency and reduce pellet damage and drag - but unlike most of the people fawning over it, I do know enough physics that there is no way in hell I am believing half the crap that's being said.
Heck, I still want one of the barrels, but as a scientist and engineer, I've set reasonable expectations for what it can actually do.


However, back to the point - assuming a rigid barrel can be mustered, even a smoothbore should group moderately well at up to 20 yards or so - so you should be able to move back quite a bit.
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Unread postAuthor: Floyd » Sat Nov 01, 2008 3:37 pm

So I took Noob's advice and built a springloaded trigger system.
I used a strip from an old car inner tube as the spring which is triggered by a pin being pulled and the rest is pretty self explanatory.

The vid is still being processed.
[youtube]http://www.youtube.com/watch?v=LL6xIBwOKOY[/youtube]

Also anyone else here use a comcast email? PCGuy told me spudfiles is on their spam list. Anyone know anyway to change that? If not maybe we could all email comcast and complain or something.
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Unread postAuthor: FordGtMan » Tue Nov 04, 2008 11:27 pm

Late post but o well. That "spring loaded" system you have there probably wont increase performance at all because of the speed the valve is moving. Looks to slow to be effective in any way. Maybe a larger spring?
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 05, 2008 1:33 am

Agreed with the above, while ingenious, your system isn't exactly knocking the valve open. Have you trued lubing it to cut down on friction?
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