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Semi-Auto Pneumatic Design

A place to ask general spud cannon related questions.
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Semi-Auto Pneumatic Design

Unread postAuthor: PaulsAirsoftArmory » Tue Mar 03, 2009 8:35 pm

I saw the design listed here: http://www.spudfiles.com/forums/revised ... 17540.html and decided to improve upon it significantly.

It would use air as a power source and would probably shoot golf balls (unless I need to scale it down to marbles). Basically, each time the valve (trigger) is released, air forces the golf ball down the barrel and at the same time cause the bolt to move backwards and load a new round.

I may need to revise the design by removing pipe "3" and opening part of pipe "1" to have the air travel directly into the barrel, instead of in a complicated "U" shape.

The front of the bolt:
<a href="http://s614.photobucket.com/albums/tt229/PaulsAirsoftArmory/?action=view&current=NewPotatoCannon1.jpg" target="_blank"><img src="http://i614.photobucket.com/albums/tt229/PaulsAirsoftArmory/NewPotatoCannon1.jpg" border="0" alt="Photobucket"></a>

A view from the side. NOTE: numbers "2" and "3" are switched. It should follow the order in the first picture.
<a href="http://s614.photobucket.com/albums/tt229/PaulsAirsoftArmory/?action=view&current=NewPotatoCannon2.jpg" target="_blank"><img src="http://i614.photobucket.com/albums/tt229/PaulsAirsoftArmory/NewPotatoCannon2.jpg" border="0" alt="Photobucket"></a>

A view from above:
<a href="http://s614.photobucket.com/albums/tt229/PaulsAirsoftArmory/?action=view&current=PotatoCannon3.jpg" target="_blank"><img src="http://i614.photobucket.com/albums/tt229/PaulsAirsoftArmory/PotatoCannon3.jpg" border="0" alt="Photobucket"></a>
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 03, 2009 11:23 pm

Seems like a needless complication compared to the blow-forward bolt - unless I've completely missed the point.

I saw the design listed here and decided to improve upon it significantly.


That design involves a hammer valve that is triggered every time the bolt returns, so I don't really understand how you've improved it by removing this crucial element. Otherwise it would have worked just as well like this:
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Unread postAuthor: POLAND_SPUD » Tue Mar 03, 2009 11:36 pm

@jsr
I agree it has nothign to do with the design he mentioned
but no, it's not a blow forward bolt (at least the way I see it)

it's just a little bit overcomplicated design which aims at using air pressure from the barrel to cycle the gun

basically it's the same thing as this ->> http://www.spudfiles.com/forums/gas-ope ... 17542.html

@PaulsAirsoftArmory check the thread mentioned earlier to see why it's not the best idea

if you want to do it you can use a simple T to do the job... Iam sure that JSR can provide you a pic of his attempt at a similar design
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 03, 2009 11:44 pm

POLAND_SPUD wrote:no, it's not a blow forward bolt (at least the way I see it)


Well fair enough, it's a blow back bolt ;p

Have a simpler one:

Image
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Unread postAuthor: inonickname » Wed Mar 04, 2009 2:42 am

POLAND_SPUD wrote:it's just a little bit overcomplicated design which aims at using air pressure from the barrel to cycle the gun

Like this perhaps?

My design(or whoever came up with it before me..) revolves around the principle of using the motion of the bolt to control ammunition feeding and valve timing.

Still, it's a good design but as I understand it you would need a very uniform projectile that's an extremely good fit in the barrel, a very smooth piston et cetera.

It's always good to see people thinking, so keep it up and keep developing on it :twisted:
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Unread postAuthor: POLAND_SPUD » Wed Mar 04, 2009 9:44 am

well your design is superior to this becasue the piston is large.. whereas here it's smallish... obviosuly the design would mostlikely work better with a large piston

both of the designs are blow back bolts but yours is better becasue
revolves around the principle of using the motion of the bolt to control ammunition feeding and valve timing


I think it's good to try new things... unfortunatelly not every design will work and some would work better than others and would be easier to implement

if you want to experiment with designs go for it.. but if you want to build a semi that works then copy the design I (and several other members) built


I don't want to praise 'my' design and turn this discussion into something like 'mine is better than yours'... becasue it's all about improving things for the good of the community - not about competition...

if someone can design (and build) something that both:
offers better performance than the design I used and at the same time is easy to implement I'd switch to that design but so far 'mine' (I think that the first person who proposed this was al-xg but I am not sure) is still the best in both areas
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Unread postAuthor: PaulsAirsoftArmory » Wed Mar 04, 2009 7:21 pm

Note the "Significantly" in the first sentence. The other design gave me inspiration for this design. Mine is a completely different design.

It wouldn't actually use the pressure from the barrel (as in a gas operated rifle), but two separate air chambers connected to a set of parallel valves, one for the barrel, and one for the guide rod. I know I didn't illustrate it, sorry. It is similar to the blow back design illustrated above, but more pressure/air is used for the actual propulsion of the round compared to the backwards motion of the bolt itself.

This design, if done correctly, would be more efficient than a normal blow back design, such as above. It could be even more efficient if I locked the bolt forward, used one valve to fire the round, unlocked the bolt, and then used a second valve for the guide rod. Almost like some sort of bolt action/semi auto design, with three steps. I know it sounds complicated, but I think I could get it to work.
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Unread postAuthor: POLAND_SPUD » Thu Mar 05, 2009 1:17 am

It wouldn't actually use the pressure from the barrel (as in a gas operated rifle), but two separate air chambers connected to a set of parallel valves, one for the barrel, and one for the guide rod. I know I didn't illustrate it, sorry. It is similar to the blow back design illustrated above, but more pressure/air is used for the actual propulsion of the round compared to the backwards motion of the bolt itself.

so it's like mine.. but mine doesn't have two chambers for it, two 90 degree bends and two valves... one firing valve, one 90 deg turn and one chamber is enough
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Unread postAuthor: MRR » Thu Mar 05, 2009 2:23 pm

I was also thinking about a blow forward bold and came up with an idea that might work without losing much performance.

Image

For the shape I would use a little funnel and cast it in epoxy.

BTW which rings are bigger?
a: blue circle
b: green circle
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Unread postAuthor: roboman » Mon Mar 09, 2009 9:25 pm

Neither; they're the same size. I'm confused as to how your design would work. Could you please provide an explanation?
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Unread postAuthor: SEAKING9006 » Mon Mar 09, 2009 9:43 pm

I would just modify a bolt action mechanism (one that goes the PROPER way, not bass-ackwards like HEAL or something.... no offense, I hate moving barrels) by drilling holes into the bolt and filling the back end of it with mighty putty. Place the airflow input over the holes in the bolt, and add a spring. As long as you can build a simple replica of an integral magazine of an old bolt rifle, you're in business.
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Unread postAuthor: Hotwired » Mon Mar 09, 2009 11:09 pm

The proper way?

Are we meaning the proper way for a bolt to move when it's loading, firing and ejecting cases for self contained propellant and projectile?

Or are we talking about a two part system where the propellant is kept separate from the projectile by a large mechanical valve and thus requires at least a 90 degree turn of dead space to get a bolt in between the valve and projectile.

A telescoping barrel inside an outer barrel is the simplest way to get the least dead space and still have the function of a bolt action. It really shouldn't matter that it's being pulled the "wrong" way because for this application that's actually the "right" way.
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Unread postAuthor: POLAND_SPUD » Mon Mar 09, 2009 11:55 pm

@hotwired... true
for some strange reason quite a lot of people who want to build a semi believe that you have to directly copy the way in which some real firearm operate..

but 99% of spudguns don't use cartridges and it's not the best idea to use them (becasue you have to manufacture them somehow and trust me when I fire my semi I spend more ammo in a minute than I used to fire in an hour)

those who realize that spudguns are completelly different form firearms usually try a blow forward bolt but they don't realize that blow forward bolts will hamper performance


I don't agree that there has to be a 90 deg angle.. in fact with 'my' design you can both get rid of that and completely remove any obstruciton of the flow in the barrel.. you just have to put the air ram vertically and build a block with hole of the same ID as the barrel cut trough it... something similar was used on BTB's lever action gun...

there is another version of the same idea.. instead of moving the whole block you could have a solid bolt sliding in it and moving up and down

but I don't have enough time to build that...

EDIT
pics added
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 10, 2009 1:39 am

POLAND_SPUD wrote:for some strange reason quite a lot of people who want to build a semi believe that you have to directly copy the way in which some real firearm operate


Flying cartridges are cool, end of ;)
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Unread postAuthor: MRR » Tue Mar 10, 2009 9:55 am

@roboman
The idea of that blow forward bolt is that you have a cone with big exhaust holes at the ?edge? (green) and a negative cone (blue) with a pipe in the middle.

When you trigger your gun the blue part gets a hit forward before the air stream enters the pipe. I thought the shape of a cone would work quite well because the air flow doesn't have to make big turns.

Clide for example uses a blow forward bolt that is a pipe with entry holes so that the air have to make a 90° turn to enter the barrel.
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