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Charging handle

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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Charging handle

Unread postAuthor: FighterAce » Fri Jul 30, 2010 2:33 pm

I finished building my first piston valve and started working on the wood for my next rifle but already I hit a snag. I'm piloting the piston with a schrader valve and I use this firing pin to depress it... works just like a zip gun.

Image
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I originally planned to make a sort of a port on both sides of the rifle so I can manually push the firing pin back and rotate it to lock. I realized dirt and gunk would be able to get into the mechanism too easily so I abandoned that idea.
Now I'm looking for a way to push the firing pin back and rotate it via charging handle that will be a bit more forward so the firing pin itself is not exposed, ie closed inside the wood.

The trick is that the charging handle is not directly linked to the firing pin... to be more exact, not linked to the M4 all thread protruding from the back of the firing pin. Its because the gun could accidentally fire if the charging handle was bumped or rotated for whatever reason.
So.. If the charging handle is not linked directly to the firing pin, theres other no way it can fire... except if you pull the trigger.

Ideally it would be something caveman simple, impossible to fail but without the use of welding or glue and stuff...

Any ideas?
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Unread postAuthor: jor2daje » Fri Jul 30, 2010 2:41 pm

Do you need a firing pin to depress a shrader? Wouldnt it be a lot easier just to use a hammer, or even a simply lever trigger, even at high pressures they are easy to open.
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Unread postAuthor: FighterAce » Fri Jul 30, 2010 2:54 pm

I went with this design for consistency and an easier trigger pull because this will be installed in a sniper rifle... most important... the firing pin and the actual trigger are very far apart and theres no "direct route" so theres a lot of bends and twists and so on.
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Unread postAuthor: jor2daje » Fri Jul 30, 2010 2:56 pm

Ok, i would still consider something lighter, a firing pin with that much mass and such a large spring would probably go through schrader cores pretty quickly.
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Unread postAuthor: jrrdw » Fri Jul 30, 2010 3:05 pm

Cloths hanger linkage (wire), a bell crank or two. Could be easily hidden and work well if there isn't any slop in the set up.
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Unread postAuthor: FighterAce » Fri Jul 30, 2010 3:08 pm

Well.. I've done some tests and if I shorten the spring for about 1-2 cm, it will not open the schrader at 30 bar, and I plan on going up to 40 bar.

I already considered the schrader cores failing and if this becomes a too big of a problem in the future, I'm going to replace the triggering schrader with a homemade push button valve with a bigger vent hole, a bigger spring... basically all beefed up parts. But I'm hoping I wont need to do that.
So far I've had about 100 discharges with the setup and no signs of wear yet.

Edit. Dam you're fast :D I dont think cloths hanger wire is strong enough, I'd prefer to go with machined stainless steel or something. We only have plastic coat hangers around here anyways... but from I've seen how easily the wire ones bend, I dont think its strong enough.
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Unread postAuthor: ramses » Fri Jul 30, 2010 3:22 pm

I think you should go to a straight pull mechanism and use a separate sear that holds the firing pin back. That way, the linkage could be as simple as a slot that the current handle rides in attached to a separately spring loaded charging handle.

    pull charging handle back,
    charging handle pulls hammer/pin
    sear catches the hammer/pin,
    let go,
    spring pulls charging handle back.
    pull trigger,
    hammer moves forward,
    hits the schrader,
    hammer/pin comes to rest near the end of the closed off slot.
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Unread postAuthor: jor2daje » Fri Jul 30, 2010 3:23 pm

grab some stainless welding rod, they come in different diameters and would be plently strong enough for a schrader.
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Unread postAuthor: jrrdw » Fri Jul 30, 2010 3:33 pm

With the pictured set up, does the clamp get knocked off the sleeve? On the other side of troubles, does the clamp pinch the sleeve causing the 'hammer' to jam before the end of it's travel?
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Unread postAuthor: FighterAce » Fri Jul 30, 2010 6:31 pm

ramses wrote:I think you should go to a straight pull mechanism and use a separate sear that holds the firing pin back. That way, the linkage could be as simple as a slot that the current handle rides in attached to a separately spring loaded charging handle.


Unfortunately there is no space under the schrader to do that... the stock is filled up completely. I really wanted to do that but I need all the stuff in the stock... dont want it front heavy at all.

jor2daje wrote:grab some stainless welding rod, they come in different diameters and would be plently strong enough for a schrader.


Not sure how they bend.. but from my experience, when you bend something and then have large amount of force bending it further in the same direction when its in use, that part will fail.

jrrdw wrote:With the pictured set up, does the clamp get knocked off the sleeve? On the other side of troubles, does the clamp pinch the sleeve causing the 'hammer' to jam before the end of it's travel?


The clamp holds the copper part on the schrader. The travel of the firing pin is just 1cm from the locked position (for reference, the piece of all thread is M4 ie 4mm) so the clamp doesnt effect its travel at all.
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Unread postAuthor: FighterAce » Sat Jul 31, 2010 4:53 pm

I cant believe out of so many innovative minds around here nobody has an idea...
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Unread postAuthor: sinper2006 » Sat Jul 31, 2010 6:45 pm

what about something like this?
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Last edited by sinper2006 on Sat Jul 31, 2010 8:08 pm, edited 1 time in total.
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Unread postAuthor: Lockednloaded » Sat Jul 31, 2010 6:56 pm

Or some sort of setup like a click pen. Take apart a spring pen and supersize some of the parts to replicate the setup. If you can manage it it should work great.

Or you could just have a actual large pen depressing the schrader with the ink tube removed and replaced with a rod
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Unread postAuthor: ramses » Sun Aug 01, 2010 11:52 am

FighterAce wrote:Unfortunately there is no space under the schrader to do that... the stock is filled up completely. I really wanted to do that but I need all the stuff in the stock... dont want it front heavy at all.


But the sear would be significantly behind the schrader, at the back of the hammer's travel. I'm not sure where your trigger is, but you should be able to sneak a 1/8" rod in there somewhere to link the trigger to the sear. You still need a trigger somewhere.
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Unread postAuthor: FighterAce » Sun Aug 01, 2010 1:30 pm

sinper2006 wrote:what about something like this?
Image


Cool... at first I thought of using a piece of pipe for this but then I realized I could machine a piece of metal with ID to go around the copper housing, lower half would be like a half circle with a wall thickness of about 5mm and above, some more material for mounting the handle itself.

Image

Thanks sniper! :D

ramses wrote:But the sear would be significantly behind the schrader, at the back of the hammer's travel. I'm not sure where your trigger is, but you should be able to sneak a 1/8" rod in there somewhere to link the trigger to the sear. You still need a trigger somewhere.


I mean... there is no space at all under the schrader... not in front or behind.
I believe this zip gun mechanism is much tougher and less likely to fail, dont you think?
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