I would not put unregulated co2 inside a mag that wasn’t even designed for green gas. You’ll turn your mag into a pipe bomb.
TM mags do seem to do that. Takes ages to fill them and they hiss until they spill liquid green gas out. I don’t see it as a problem so I don’t really worry about it.
What BB’s are you using? I’ve had this issue every now and then, mostly with BB’s that aren’t Geoff’s. Not sure if it’s the coating inside he channel, but prolonged use should wear the sides smooth.