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Precharged pneumatic semi-auto *with pic of entire gun*

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Precharged pneumatic semi-auto *with pic of entire gun*

Unread postAuthor: auxiliary » Wed Jun 25, 2008 10:50 pm

I have decided to make a an airsoft gun that uses a blow forward loading and firing mechanism (similar to JSR's syringe gun) that is powered by an attached steel tank, pumped up to around 400psi with an attached homemade high pressure pump like Gippeto's stirrup pump. Here is the firing mechanism:


http://www.putfile.com/pic/8346751

When the pin on the pressure washer valve is depressed, the high pressure air rushes through, pushing the turquoise Delrin piston and green power tube forward. As it goes forward, the green tube pushes the BB forward. When the Delrin piston reaches the hole in the aluminum tube that surrounds it, the air seeps around the o-ring on the piston and rushes into the hole in the green power tube. The air going through the green power tube propels the BB. The blue return spring pushes the piston back until another BB is loaded.

I either have or can easily purchase all of the parts in this diagram, but I don't know of anything that can work as the green power tube except for brake line which I don't know where to get. I will make a picture of how the entire gun will look like with the air tank/s and on board high pressure pump. I can either make this gun a bullpup or traditional rifle configuration.
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Last edited by auxiliary on Sat Jun 28, 2008 11:18 am, edited 1 time in total.
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Unread postAuthor: THUNDERLORD » Wed Jun 25, 2008 11:43 pm

Very nice diagram.
I don't see how the bolt will return automatically unless you plan on giving the pressure washer valve quick taps?

Maybe the green power tube could be constructed from brass tubing found in hobby shops. They can be nested together sometimes.

Perhaps someone near where you're at can be more helpful which auto-parts stores carry brakeline.

It will need to be a snug fit to the ID 6.03mm barrel so you might need to machine something or put the tube in a drill chuck and grind/sand it down to proper diameter.
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Unread postAuthor: psycix » Thu Jun 26, 2008 7:11 am

Might work, only problem I forsee is the flow restriction during the "seeping around the o-ring"
I hope you will get it to work!
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 26, 2008 7:24 am

That bolt is going to be under a lot of strain, make sure it's sturdy!
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Unread postAuthor: Tom » Thu Jun 26, 2008 7:58 am

I think that when he talks about delrin he is going to machine it , delrin is a great machining plastic(in mine opinion :D ). Did you made that diagram by yourself looks very professional :!: .
It would be cheaper is use less copper pipes anf fitting over the bike-pump tube. Just like JSR said"make sure it's very sturdy!" :D
G's from the Dutch, Tom
PS: How is your semi-automatic pro-pain gun project going :?:
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Unread postAuthor: auxiliary » Thu Jun 26, 2008 12:10 pm

THUNDERLORD: To make the the piston move back without letting air continue to go through, the pressure provided by the pressure washer gun valve will have a force that is the average of the extended spring tension and the compressed spring tension. Meaning... when the piston moves forward, it has enough pressure behind it to push the spring back and have enough momentum to go pass the hole, but not enough pressure force to hold back the spring when it is fully compressed making it stay behind the hole. I will do this by getting a very strong spring and limiting the airflow of the pressure washer gun little by little by limiting the trigger pull to get the perfect adjustment.

I checked my local Tammie's Hobbies, but I couldn't find anything. I guess I will just keep on searching. Also the power tube doesn't have to be very exact because I will probably put an o-ring in the loading chamber somewhere.

psycix: The Aluminum tube I have is thick enough to where the relief between the 1/2in. copper tube and the o-ring is sufficient. Plus I'll make sure to make a lot of holes :P

JSR Delrin is pretty strong stuff (a metal substitute :shock:) and plus there are two rubber bumpers so I think it will be fine.

Tom: Ya I have a fancy drill-on-a-vice lathe and an old file so I can shave the Delrin pieces effectively. And I'm pretty much the MS paint master... The only pipe that my Aluminum bike pump tube fits in is the 3/4in. copper tube (very nicely too) so I have to work around that. My pro-pain project went in the dumps because I spent a lot of time making the parts and halfway through I realized that the design just wasn't going to work so I gave up. Plus 40-90psi propane can't cause as much pain as 400psi :twisted:

Here I have the picture of the gun with all the fittings that make up the tanks and pump that create the general body of the gun. Light gray fittings that make up the tanks and stuff are 3/4in. galvanized steel fittings (except for the tank of course). The pump is 3/4in. copper pipe (same as outer barrel) with brass female adapters that will encase a check valve and then connects to the ball valve and leads into the tank.

I decided to make the entire length of the outer barrel 3/4in instead of reducing to 1/2in. because it would make it easier to build the blow forward valve and the magazine well. I plan on making the mag well by heating and bending HDPE (high density polyethylene) or sea board around the copper that surrounds the blow forward valve and making a rectangular cup at the bottom by epoxying other rectangular pieces to the bend piece.
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Unread postAuthor: pocket » Mon Jul 07, 2008 10:25 am

lol wow thats scary your working on the same thing as me except mine will be suit to look like an M4 with a 14" x 7/32" with a 1/2" copper pipe sleeved barrel im curious though on how you were planing to get your mag working
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 08, 2008 5:25 am

pocket wrote:im curious though on how you were planing to get your mag working


I'm guessing from the diagram that it's a commercially available existing magazine from an airsoft rifle.
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Unread postAuthor: Tom » Tue Jul 08, 2008 5:31 am

jackssmirkingrevenge wrote:
pocket wrote:im curious though on how you were planing to get your mag working


I'm guessing from the diagram that it's a commercially available existing magazine from an airsoft rifle.


That has two lids where the BB's come out of the magazine, the power tube will move forward when activated. Collecting one BB out of the lid, then the valve realeases air. The power tube moves back and a new BB pop up in the lit waiting to collected :D .
G's from the Dutch, Tom
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Unread postAuthor: auxiliary » Tue Jul 08, 2008 11:35 am

pocket wrote:lol wow thats scary your working on the same thing as me except mine will be suit to look like an M4 with a 14" x 7/32" with a 1/2" copper pipe sleeved barrel im curious though on how you were planing to get your mag working


I have a G&P M16 180 round AEG mag and I will make the mag well out of a bent piece of poly board or some other plastic and make two other walls to make a cup for the magazine to go into. Like this:
http://www.putfile.com/pic/8404118
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