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All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: Arsenul on January 28, 2017, 10:28:22 AM
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To start, I'm terrible at wording things when it gets technical, so please tell me if you have a question and I'm sorry before hand.
Hoping to create a Air Bow mainly for fun target practice while camping, shooting arrows for fishing, and maybe hunting something as big as a rabbit. I don't have big plans for the Air Bow I plan on making, as long as it shoots a arrow fast and like 20'. With that in mind! I'm planning on making this a PCP. I'd like to find a air cylinder that will fit the needs I have pretty well, a air pressure regulator to control the amount of air released, and get the right trigger assembly for the air bow. My question to you is a little confusing so I'll try to word this as best I can.
I need to know the airflow path that goes through this and how the trigger assembly works with it. I'm also curious how the trigger assembly works with airflow, and what I can do with that to shoot a arrow from a tube. Also what parts NEED to be in a PCP to allow air to pass through the gun and actually fire?
Again, sorry if I worded things wrong.
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First thing.... be VERY careful what arrows you use.... CF arrows are NOT designed for internal pressure, so if you are thinking of sliding them over a thin "barrel" use aluminum.... I wouldn't want to see one explode and drive CF splinters through your hand....
As far as the airflow, there is a valve opened momentarily by a sliding hammer strike, and the hammer is released by the trigger.... The hammer is powered by compressing a spring.... Look at a parts diagram for a Discovery and you will see how it works.... I would suggest you start with an existing, SAFE design, HPA is not something to play around with if you don't know what you are doing....
Bob
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I think the largest hurtle many face with Air Bows is that of air use with the 2 primary design types.
1st type being that of a more conventional PCP gun using a soda straw barrel / guide with an Aluminum arrow slid down over it.
2nd type being based upon a BIG BORE barrel an arrow can slip inside of with fetching rolled/bend over a tad.
In the type 1, your faced with HUGE volume between valve and barrels muzzle where the end of arrow sits before shot. This ENTIRE VOLUME must be pressurized effectively to get arrow to launch with any degree of effective velocity. As arrow starts to move the Volume increases further absorbing the expanding air pressure driving it.
Doing this takes a valve that FLOWS A LOT of air ! ... Muzzle report will be rather loud too.
In the type 2, Said arrow has a small sealing piston or ring in place of the Nock ... a Guide ring or fingers to hold it centered at muzzle one place down the I.D. of a big bore barrel.
This configuration operates like a conventional PCP in that Valve to projectile distance before firing is very short and of small volume. Now upon shooting arrow it is propelled similar to a pellet or bullet and can have much increased efficiency in using the pressure & volume of air released to generate velocity & power to the arrow.
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First thing.... be VERY careful what arrows you use.... CF arrows are NOT designed for internal pressure, so if you are thinking of sliding them over a thin "barrel" use aluminum.... I wouldn't want to see one explode and drive CF splinters through your hand....
As far as the airflow, there is a valve opened momentarily by a sliding hammer strike, and the hammer is released by the trigger.... The hammer is powered by compressing a spring.... Look at a parts diagram for a Discovery and you will see how it works.... I would suggest you start with an existing, SAFE design, HPA is not something to play around with if you don't know what you are doing....
Bob
As a safety precaution, the first few firing tests will either be in a forest or field, away from people. If possible it will even be done inside a container of some kind or room. Also will be fired remotely or via a pulley and string. I've seen what air can do to people when it goes wrong and I don't want that to happen to me.
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In the type 2, Said arrow has a small sealing piston or ring in place of the Nock ... a Guide ring or fingers to hold it centered at muzzle one place down the I.D. of a big bore barrel.
This configuration operates like a conventional PCP in that Valve to projectile distance before firing is very short and of small volume. Now upon shooting arrow it is propelled similar to a pellet or bullet and can have much increased efficiency in using the pressure & volume of air released to generate velocity & power to the arrow.
Forgive me if I misread, but it sounds like you're talking about how the arrow is positioned on the tube/barrel. If that's the case I was planning on making the arrow slide onto the barrel easily but near the back of it, where the arrow would stop, would be a thicker piece of metal. This would allow it to be seated firmly and stay in place. So that only the release of air shoots it forward. Again, I could be wrong with how I read that.
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In the type 2, Said arrow has a small sealing piston or ring in place of the Nock ... a Guide ring or fingers to hold it centered at muzzle one place down the I.D. of a big bore barrel.
This configuration operates like a conventional PCP in that Valve to projectile distance before firing is very short and of small volume. Now upon shooting arrow it is propelled similar to a pellet or bullet and can have much increased efficiency in using the pressure & volume of air released to generate velocity & power to the arrow.
Forgive me if I misread, but it sounds like you're talking about how the arrow is positioned on the tube/barrel. If that's the case I was planning on making the arrow slide onto the barrel easily but near the back of it, where the arrow would stop, would be a thicker piece of metal. This would allow it to be seated firmly and stay in place. So that only the release of air shoots it forward. Again, I could be wrong with how I read that.
I get that ... A SHAFT over the TUBE design is basically CORKED at muzzle by the shaft slid over it.
It is the space down entire length of support barrel that must be pressurized to impart expansion energy of the air to start pushing the arrow shaft off of it.
Another point ... is say air hole on barrel is 3/16"" I.D. and OD is closer to 5/16" .... As barrel starts to move the air pushing on arrow shaft expands to fill this 5/16" space opening up as shaft starts moving. The AREA increase per inch of shaft sliding off the barrel is HUGE. The losses in pressure driving the arrow as the volume increases make this type design not very efficient.
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Yes, just before the arrow leaves the front of the guide tube, you have filled the entire volume of the arrow (5/16" ID) through a 3/16" hole.... not an efficient design.... and you are pressurizing the inside of the arrow, something it was not designed for.... IMO it is only a matter of time before we see some serious injuries as a result of this type of design with carbon fibre arrows designed to be strong when you push on the end of them, but not designed to contain internal air pressure.... Just because it works once, doesn't mean the arrow will survive 10 shots.... or the next one if its structure is compromise from glancing off something hard....
Bob
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Air Venturi announced the release of .25 .357 and .45 cal air bolts at this years shot show . Just need to get a rifle and your set. Not sure when they'll be available for purchase though.