I am not a pneumatic expert but I did convert a wood mortising machine to pneumatic power down and up feed.
A few things I learned:
1) How much force do you need to push the bullet through the sizing die? I don't know how to measure this??? Maybe put a bathroom scale on top of the press ram and put your weight on the scale until the bullet is pushed though the die.. reading the highest weight the scale registers. Lets say it takes ~110lbs of force to push the bullet through the die???
2) What size pneumatic cylinder do you need? The amount of force a cylinder will put out is equal to the surface area of the piston face X the PSI of your air supply. So lets start with a cylinder that is 1.6" dia. (1/2 X 1.6") ^ 2 x 3.14 = 2 square inches of piston face surface area. At 55psi x 2sq-in = 110lbs of force. A good starting point!
3) I would recommend a power down stroke with a spring return. It is a lot more complex to power the down stroke and power the up stroke (with a mortiser you have to push the square chisel down through the wood then pull the chisel out of the wood and overcome the large amount of friction between the chisel and the wood. I went powered down/up and it meant a more expensive control valve and considerably more complex plumbing)
4) I would recommend a double acting piston even though you will only be pressurizing one side of the cylinder.
5) Plumb your compressor to the control valve then from the control valve to the power side of the cylinder. Open the control valve and "
BAM!!!" the piston shoots to the other side of the cylinder like a .... well.. bullet! You need to dampen this so it doesn't shoot so fast and has more of a controlled feed.
6) Put a needle valve between the control valve and the cylinder. This will limit how FAST the air will enter the cylinder and limit the acceleration of the piston. The piston will now accelerate a lot slower but will continue to accelerate through the cycle. Now you need to decelerate the piston at the other end of the stroke.
7) Plumb the other side of the double acting piston to a second needle valve then vent the far side of the needle valve to the atmosphere. Now the piston will start to accelerate but the second (cushion) needle valve will limit how fast the air escapes from the cylinder on the opposite side of the piston cushioning the end of the piston stroke.
8) You are ready to go into action. Open the control valve. The piston starts at a moderate speed and accelerates. At about 2/3rds of the stroke the piston will start decelerating. When all the air escapes the far side the the cylinder it will be exerting 110lbs of force on the ram --> pushing the bullet through the die.
9) Release the control valve. The pressure in the cylinder will decrease until the piston / ram starts to rise under the force of the spring. The first and second needle valves will control how fast the air exits the power side of the cylinder and how fast it enters the other side of the cylinder. Giving you a nice smooth upstroke and preventing a return "
BAM!!!"
10) The ram won't push the bullet through the die? Increase the pressure from 55lbs to 80lbs??? Higher pressure = 160lbs of force.
11) The ram travels down or up too fast or slow? Adjust the needle valves until you get a stroke you are happy with.
12) Use a foot actuated control valve... this will leave both hands free to work.
13) These are the pneumatic fittings you want to buy on ebay. Just push the tubing into the hole in the blue plastic and the tubing will hold. Push down on the blue plastic and the tubing will be released and come out freely. I have some all plastic connectors that have worked well for me, held up without issue and are a lot cheaper.
14) Why does the ram in the press in the video have to travel ~3" - ~4"? It seems like 1" of ram travel should be plenty?
Like I said I am no expert, this is just what I have learned from building my powered mortising machine. Take it for what it is worth.