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Hello, first of all sorry for my bad english but I'm not american...I've come across this site looking for parts for my airsoft svd dragunov (which I use mostly for plinking) and what can I say...I think i'm addicted.
So what I want to do as a start is to build a BB "single shot" shooter, capable of shooting anything between 0.2g airsoft bbs to 0.88g steel bbs.
Ideally it should resemble a sniper rifle both in looks and functionality.
I've seen a lot of great designs here, and I've educated myself a bit: what I've come up with is schematized in the attached drawing:
From left to right: a sodastream or other suitable CO2 tank attached to a brass T in which the lower hole is attached to a schrader valve which will be used to fill it with air coming from a fridge compressor. Next I plan to use a Co2 pressure regulator (I've found some regulators for welding TIG capable of several thousands psis in the inlet, are they ok?) which will fill the shooting chamber at variable pressure (low for plastic BBs, higher for steel ones). Before shooting, I plan to cut the communication between tank and shooting chamber by using a ball valve.
The firing mechanism should be represented by a 1/4 or 3/4 QEV (I have no idea which is best) piloted by a (modded) blowgun.
The barrel is going to be a precision brass barrel for airsoft which I already have, it can be fitted with its original airosft hopup rubber, but I wonder if it will be suitable for heavy bbs and huge pressures (say 200-300 psi), so I still need to define wether the hopup will remain stock or if I have to make a new, metal one close to the end of the barrel.
As for BB loading, I still have no ideas. I'm ok with having to put a bb manually each shot but that's about it. Bolt action? Breech loading?
Any suggestion is VERY appreciated, I'm not even sure if this is going to work!
Starting from the top...
The schematic looks like it would work. I would avoid brass in a very high pressure build like this, but that's just me.
A 3/4" QEV will have much better flow than a 1/4" QEV, go for the 3/4" if you can get it.
200-300psi is not very high for metal connections, provided they're not labeled as low-pressure or Schedule 10 (And even so steel schedule 10 steel fittings are good way past 300psi). A welding regulator should work fine. The argon that's probably designed for is stored at much higher pressure than CO2.
I can't say much about the location of the hopup, having little knowledge in that area myself, but I'd recommend keeping the hopup pretty far away from the muzzle, or you're likely to cause the BB to "hop" much farther than intended.
A TIG welding regulator is more likely a flow meter-won't work. If it is in fact a pressure regulator it is not going to have ASA-paintball threads. There are some C02 adapter to connect ASA to the CGA threads on the welding regulator-typically found and used for home brewing equipment. I think the tank fitting are different on Argon and C02 for welding applications so you may need a different input fitting or an adapter on you regulator
if you can get a grip on the CO2 tank take the asa valve off and replace with 3/8th inch flare fitting worked for me
most big random like i ever seen
thanks to all for the comments
@seafroch: I planned to use brass just because it's the material in which I've found pneumatic fittings to be most readily available, but I wouldn't mind spending a bit more for steel ones, if I can find them. Do you think brass can explode or something like that?
Hopup: in fact on airsoft guns the hopup is at the very start of the barrel, I think this is the most effective location. The end-of barrel metallic hopup is something I've seen in the Hubb Library.
This is going to be the last thing to make experiments with. I'm thinking about using a bicycle brake pad of sintered material instead of rubber, this should last more and work even with metallic BBs.
@metalmetr: the regulator I've seen is this: Ebay Link, the right translation of what it's called here is "pressure reducer MAXY WIKA CO2/Argon-TIG,MIG/MAG.
In fact, I don't know much (yet) about different threads and adapters...if I can use this, it would be nice because it's pretty cheap compared to some co2 regulators I've seen which cost 10 times the price.
@cannon monkey: sounds ok, thank you
With some simple mods (a pinhole in the diaphragm and a spring behind it) you can hook up your resevoir to the chamber side of the QEV without needing the extra ball valve.
I'm not sure to understand your suggestion: for "reservoir" you mean the regulated shooting chamber or the HPA reservoir?
The fact that the valve is momentary is a form of "regulation" itself, as in you could hook it up directly the HPA supply, and by reducing the valve opening time you could get the same power but also achieve air economy.
This is an inefficient (because you're dumping extra air from the feed through the pilot) way of doing it, but it works if the gas flow is lower than the pilot. Alternatively, a 3 way pilot valve will shut off the gas feed while the pilot is exhausting, or you can mod the QEV as described earlier and have the gas feed replacing the elbow and cap in the above diagram.
Sorry to be the bearer of bad news but that "regulator is actually a flowmeter. If you look in the enlarged photo you will see L/min in the gauge in the right. If it was a pressure regulator it would have a gauge similar to the left gauge for a lower pressure range. The left gauge indicates tank pressure.
The right is the output gauge and that gauge indicates a rate of flow not a measurement of pressure.
It actually is a regulator, but with a flow gauge on the output as opposed to a pressure gauge. "Riduttore di pressione" means "Pressure reducer"
Edit; JSR beat me to this while I was finding a photo.
Most TIG welding regulators are indeed pressure regulators. Depending on the model of the welder, it is either a fixed pressure regulator (Preset and not adjustable) or a pressure regulator with a needle valve and flow meter.
In the fixed regulator the pressure is set so the flow is constant while you are welding and the flow is stopped by the welder when there is no welding current. The regulator prevents the flow from reducing as the bottle pressure drops. The welder contains a metering orifice as part of the gas valve assy.
Note this has a pressure regulator and a flow control and flow meter. It does not have user pressure adjustment on the regulator.
The one from E-bay is adjustable flow not pressure as well.
The red circle show the only adjustment on the flow meter-the flow adjustment needle valve.
The pressure adjustment is under the brass cap on the bottom. Under it is an adjustment screw. This is factory set. I don't know the setting, but it is under 100 PSI.
Can that be adjusted by the end user?
I was never aware of such an adjustment on that style of flowmeter.
@JSR: I've understood now your suggestion, as this is my first build I'd like to keep it as simple as possible (within my requirements) avoiding moddings for now, so I think I'll go for the 3 way pilot valve (I still have to find a place to buy it, in Europe I've found technobotsonline.com but I'll look at local suppliers of pneumatic equipment too).
@metalmetr, Technician1002: Ok so this isn't going to fit...Given that I'd like it to be adjustable on the fly with a knob, accurate and consistent to ensure maximum shot precision and small groupings..the only option left is a acquarium co2 regulator (~100 euros) or is there a cheaper alternative? It puzzles me that this kind of stuff is so expensive when these flow regulators, very similar in materials and constructions are dirt cheap: maybe it's a marketing thing to rip acquarium enthusiasts off?
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