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# super airsoft gun back pack mounted awesomness Answered

hello I need some help concerning the creation of my super BBMG (bb machine gun) you see I have a green medical regulation aluminum oxygen cylinder (see picture, it is about 3 feet tall and about 3-3.5 inches in diameter) and I am wondering if I pressurize it to 100 psi how long would I be able to maintain a steady rate of fire? Also, my bbmg is made of 3/4 inch pvc pipe and is about 4-5 inches long not including barrel the air inlet is a blow gun valve with a opening the size of a airsoft BB the actual bb outlet is of the same size as the air inlet only the barrel is 3 feet long (I don't think the barrel length will affect the over all time of sustained fire but I don't know for sure) if anyone can help me with this I would be extremely appreciative thanks, fidgety2

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As far as weight to volume ratio goes you would be better off getting a 5 gallon air tank they are relatively cheap, come with a pressure gauge, and a safety blow off valve so you can't over fill the tank.  If you have the cash to spare you can get a 20oz co2 tank and regulator for less than 100\$ at some chain hardware stores.

where did u get the air canister at only 100 psi without a regulator you wont get a long fire time. What type of machine gun are you using

Are you planning to just turn on the air and spray a stream of bb's?
Do you plan to use a hopper?
What will keep the air from blowing the bb's back up the hopper tube?
If the valve can't be opened and closed very quickly, you wont be able to fire more than one bb at a time...

volume of a cylinder is = (3.14r2) x h.

then knowing p1, p2, and v1 you can solve for v2
P1V1 = P2V2

with some fancier math, you could figure out how long the tank would last based on mass of the projectiles and the force of the gas over time, but its easier and possibly more effective to just experiment.

remember that as the tank empties, there will be less pressure, and therefore you will need to leave the valve open longer to accelerate the bb to the same speed down the barrel.

It would take some very fancy machining to actually make an efficient airsoft machine gun. That's why it costs so much to buy one.

interesting, my height ended up as an exponent on the volume formula...