Pneumatics in feathers.

Using standard low pressure pneumatics is possible, but it's a heavy and large way to build. Can you give us the size and weight of your ram?

Most succesfull pneumatic featherweights use a CO2 paintball bottle for gas storage. This because they are easy to aquire and are perfect in the rules.
But there are machines that use a 12 or 24V "car tyre inflator" compressor.
Regulating CO2 from the paintball bottle.
2 main options if you're not an experienced engineer/pneumatics user.
Paintball regulator or Trevor regulator.
Trevors are custom regulators for RW, quite a few in use, but not easy to aquire.

Adapting a small industrial regulator is possible, but again, heavy and large.