to switch firing modes its B but, not all weapons have optional firing modes. the Night Hawk shotgun is full auto only. the carbine and AR I've used had auto and semi auto options. the T1 Cycler and the RF-3 are both auto/semi auto. the other medic gun, I don't recall the name ATM. it has a burst fire mode, and I've never used it but it may have a semi auto mode. but, when looking at the weapons on the store, it lists the firing modes.