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Pressure at the muzzle when projectile leaves?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Pressure at the muzzle when projectile leaves?

Unread postAuthor: boyntonstu » Fri Nov 13, 2009 9:27 am

For maximum power do we want a lot of pressure at projectile exit?

What is the pressure point of diminishing return?
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Unread postAuthor: Gippeto » Fri Nov 13, 2009 10:30 am

Do some modeling in ggdt Stu.

The point of "diminishing" returns is subjective. Some people don't mind "extra" pumping for a more powerful shot...some do.
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Re: Pressure at the muzzle when projectile leaves?

Unread postAuthor: Ragnarok » Fri Nov 13, 2009 10:35 am

Obviously. For power, you want pressure to be as high as possible the whole way along the barrel to keep maximum accelerating force on the projectile.

However, for efficiency, it's bad. To have the pressure up high at the muzzle would demand a very large C:B ratio and lots of wasted air. The balance between the two is a matter of great discussion. My personal thoughts on the matter of efficiency vs. power can be found here.

It's also bad accuracy-wise. More pressure at the muzzle results in larger muzzle blast, which can knock the projectile out of whack, and cause it to tumble or spin.

For my accuracy project, the barrel will be fitted with an attachment (a combination of porting, air stripper and muzzle brake) designed to kill muzzle blast as much as possible.
Yes, I want/need high velocity, but equally I also need stable projectiles.

That said, if you're still not dealing with shoulder fired launchers, then the potential for accuracy at long range isn't anything you need to worry about.
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Unread postAuthor: kenbo0422 » Fri Nov 13, 2009 11:00 am

It's also bad accuracy-wise. More pressure at the muzzle results in larger muzzle blast, which can knock the projectile out of whack, and cause it to tumble or spin.


Would you be referring to unrifled barrels?

What about an oversized barrel shroud, like a silencer with holes in it evenly spaced and loose foam surrounded by another layer of pipe. The silencer of course, goes on the end of the barrel. It works for my other hobby, maybe it will work with this??
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Unread postAuthor: Ragnarok » Fri Nov 13, 2009 11:27 am

kenbo0422 wrote:Would you be referring to unrifled barrels?

Muzzle blast can be an issue with both rifled and smoothbore barrels.

Yes, it is more of an issue with projectiles which aren't being stabilised (either by backspin, drag or rifling), but it can still induce wobble in stabilised projectiles as well.

What about an oversized barrel shroud, like a silencer with holes in it evenly spaced and loose foam surrounded by another layer of pipe.

I've already got a design, you don't need to worry about that.
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 13, 2009 11:52 am

Image

Problen solved ;)
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Unread postAuthor: Ragnarok » Fri Nov 13, 2009 12:27 pm

jackssmirkingrevenge wrote:Problem solved

That kind of thing will not be even close to enough for what I'm doing.

Those are designed to lose an amount of gas best described in cubic centimetres, to improve grouping at a few dozen yards.

In contrast, I've got a barrel from which I need to lose multiple litres of gas, and at the same time I've got a piston valve chucking more air in at the other end - and this is so I can keep a projectile stable to its target a quarter mile away.

My solution needs to be somewhat more substantial.
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Unread postAuthor: velocity3x » Fri Nov 13, 2009 12:56 pm

Ragnarok wrote:
jackssmirkingrevenge wrote:Problem solved

That kind of thing will not be even close to enough for what I'm doing.


My solution needs to be somewhat more substantial.


Would this muzzle brake vent enough for your needs?
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Last edited by velocity3x on Wed Nov 18, 2009 10:42 am, edited 1 time in total.
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Unread postAuthor: Technician1002 » Fri Nov 13, 2009 1:37 pm

The difference in gas consumption is huge between a high muzzle pressure and a low pressure. Launching tennis balls with the 7 foot TB barrel on the Marshmallow Cannon or the larger TB cannon provides a relatively large increase in range, but the time to pump up the large cannon vs the little one is huge.

I was looking for the Marshmallow Cannon tennis ball launch photos, but I have misplaced them. I'll post them later if I find them.

Edit, found the picture of the Marshmallow Cannon tennis ball performance.
Image
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WolfCreek.jpg
T shirt cannon tennis ball range. Launched from shore. The long shot was a water filled ball. TB range is about 600 feet.
Tennis ball barrel2.jpg
The tennis ball barrel on the little launcher.
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Unread postAuthor: Ragnarok » Fri Nov 13, 2009 2:44 pm

velocity3x wrote:Would this muzzle brake vent enough for your needs?

Not really. Muzzle brakes are more to kill recoil than stabilise the projectile.

I've already mostly designed what I'm planning on using (so no suggestions are needed). It's a blend of a ported barrel, an air stripper and a muzzle brake - the latter in this case is to direct the muzzle blast away rather than kill recoil. This'll all be integral to the barrel which is using it.
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Unread postAuthor: Solar » Fri Nov 13, 2009 3:17 pm

What is an air stripper?

Sounds like a sexy stewardess on a flight to vegas...
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Unread postAuthor: Ragnarok » Fri Nov 13, 2009 3:27 pm

Solar wrote:What is an air stripper?

It's an attachment for the muzzle designed to strip away most of the muzzle blast (in an attempt to keep the projectile stable). Jack's picture is of a disassembled one (obligatory pun: Stripped air stripper.)

There's some pictures of one fitted (and one where you can see most of the design) here: http://www.samtec.hostinguk.com/photos/ ... index.html
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Unread postAuthor: Solar » Fri Nov 13, 2009 3:45 pm

So this is considered a stripper instead of a brake due to it's purpose?

Is the bore size consistent with the barrel bore?

I have seen paintball barrels both with matching bore and without.
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Unread postAuthor: psycix » Fri Nov 13, 2009 4:22 pm

Why do you need an air stripper n stuff?
Doesn't a big porting suffice or are the gases too slow to vent out?
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Unread postAuthor: Brian the brain » Fri Nov 13, 2009 5:51 pm

The gas tends to wanna go out in a cone shape.
This type of brake leaves a lot still stavelling through the center wich could disturb the ammo.
Not worthwile in a normal cannon but pinpoint accuracy over a long distance...it seems to make a lot of sense.

We'll see what it does when Rag presents the cannon..and ammo...I hope it's soon..
We might need another competition to draw him out...
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