Have the umerax mp 40 in semi/ full fire.
Buy extra mags because with a 52 round capacity mag on full auto it takes seconds to empty. Leaves a smile on your face but rounds go quick.
Also recommend a speed loader
Fun they are
I have a speed loader (could not tell you the brand) that's still in it's packaging. All I've ever used is the old fashioned thumb and index finger. My twisted way of thinking is that by taking forever to load magazines it allows the co2 temperature to warm back up a bit.