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Best way to convert this to a cartridge mechanism?

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Best way to convert this to a cartridge mechanism?

Unread postAuthor: inonickname » Sun Jul 12, 2009 7:30 am

Here's a quick full auto design I drafted.It combines the benefits of blowback (well, blow forward in this case) with the blow forward bolt. So basically; air is not recycled, firing rate is variable without massive damage to power and high pressure not required to even get average power.

The hammer and blowforward mechanism are linked. The hammer strikes the valve stem, releasing air and propelling the bolt forward. This exposes the holes in the blowforward mechanism after closing the breech, firing the round. The bolt continues to move forwards, with the blow-forward valve still open until the gas from the hammer valve is exhausted into the atmosphere. The spring then returns the mechanism, striking the valve stem.

It's a fairly good design I must say, but I'm having some problems to adapt a cartridge feed. I'd like to use the forward movement of the mechanism to select/seal the cartridge then the backwards movement to expel/eject the cartridge.

Why?
1. My ammo is long and not perfectly uniform
2. Flying cartridges = %$#&ing cool!

So, if anyone could chime in with an idea it would be greatly appreciated. Cheers
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Unread postAuthor: mega_swordman » Sun Jul 12, 2009 1:12 pm

I'm still a bit fuzzy on the details here. You say the valve is actuated by the valve stem. In your diagram, would that be the golden piece on the bottom or the red piece to the left?

Also, it looks as though the valve itself could be used for a cartridge if it were modified to be pressurized before hand. Otherwise, if you just have this valve cycling, you would just be replacing the valve on the tank repetitively for no good reason. The valve design looks nice and would work well as a fixed valve for an auto system, but as far as converting it to a cartridge, you would be best to look into other designs.
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Unread postAuthor: inonickname » Sun Jul 12, 2009 10:33 pm

mega_swordman wrote:I'm still a bit fuzzy on the details here. You say the valve is actuated by the valve stem. In your diagram, would that be the golden piece on the bottom or the red piece to the left?

Also, it looks as though the valve itself could be used for a cartridge if it were modified to be pressurized before hand. Otherwise, if you just have this valve cycling, you would just be replacing the valve on the tank repetitively for no good reason. The valve design looks nice and would work well as a fixed valve for an auto system, but as far as converting it to a cartridge, you would be best to look into other designs.


I don't mean a pre-charged cartridge, I simply mean cylindrical chambers to hold long, irregular ammunition.

The valve stem is red. In the photo it has been depressed by the hammer and is starting to allow air into the chamber. The yellow is the bolt reset.

sort of like this. The gas comes from a chamber, yet ammunition is fed from a magazine as cartridges. However, his requires manual intervention.

However, I would like something where the action is directly carried out by the mechanism.
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 13, 2009 1:10 am

You could leave it entirely up to the air, but you'd need high pressure for significant power levels.
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Unread postAuthor: inonickname » Mon Jul 13, 2009 1:17 am

jackssmirkingrevenge wrote:You could leave it entirely up to the air, but you'd need high pressure for significant power levels.


I don't think that's suitable for my application.

Basically I'm thinking:

Lets say there are 3 different sections (loading, firing and ejecting).

-When bolt is at rest a cartridge slides in
-Bolt moves forward, pushing the cartridge into the firing stage. While it is being pushed forward, it passes a detent that will catch it on the way back.
-As the bolt begins to move back, take the cartridge with it the detent catches the shell and ejects it.

I'll do some drawings.
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Unread postAuthor: POLAND_SPUD » Mon Jul 13, 2009 1:27 am

first of all, if I were you I would forget about a cartridge fed system... even the simplest designs are PITA when you try to implement them... so for now try to get it to work, when that's done you can move on to cartridges

secondly, the design seems as it might work but I don't like the fact the the hammer has to compress air as it comes back to hit the hammer valve... I suppose that momentum should help here but that might require quite a lot of tinkering with spring strength and hammer mass to get it right

what is its planned operating pressure?? and what materials do you want to use ?? and how large is it going to be??
well to tell you the truth there are almost no semiauto/fullauto guns here... the reason for this is that not every design that looks good on paper is easy to implement in real life... there are lots of things that you have to take into consideration such as friction, sealing etc.

have a look at JSR's designs - they are similar to yours to some extent and he had a lot of problems with getting things to work right...

I remember that he attempted a blowback design but he couldn't get it to work due to small piston diameter and friction... I suppose you can forget about the hammer valve (as it wastes air anyway) and try his design but with a much larger piston diameter... I've recently noticed that even with a 16mm ID you can get quite a lot of 'blowback'... if you could scale it up to 50mm or so there would be much more force to operate the blowforward bolt

you might as well, consider replacing the hammer valve with an air cylinder... I know it makes the design a bit more complicated and might require electronics and 3 or 5 way valves but in real life it easier to use something that can overcome friction with ease than to spend hours trying to minimize friction
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 13, 2009 5:06 am

I would be inclined to agree with POLSKA_ZIEMNIAKA here, it does seem a tad too complex.

the reason for this is that not every design that looks good on paper is easy to implement in real life...


Ne'er a truer word spoken. As was mentioned, you can look at my history of designs and prototypes for proof :roll: My advice would be get the valve working first, then worry about feeding your projectiles.
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Unread postAuthor: raptorforce » Tue Jul 14, 2009 12:42 am

im working on a pneumatic / bbmg it uses shells the eject and go into the barrel. you fill up the shells with a wooden slug or a bunch of bbs. i designed to be mag or belt fed but we'll see how that turns out
its almost finished im working on a bolt locking mechanism then i gotta get some hose barbs and hose and its done.
if i can post it ill show you how it works or you can see for yourself
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Unread postAuthor: ramses » Tue Jul 14, 2009 8:48 am

I think that inonickname is attempting to make something like an open bold machine gun, which is significantly easier to make than a closed bolt system, but also much less bad-ass, and harder to keep clean
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Unread postAuthor: raptorforce » Tue Jul 14, 2009 10:27 am

ramses wrote:I think that inonickname is attempting to make something like an open bold machine gun, which is significantly easier to make than a closed bolt system, but also much less bad-ass, and harder to keep clean

oops my bad lol
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