Abort a railgun or shaft firing sequence?

Can you abort a railgun or shaft firing sequence? It seems that once you enter shaft sniper mode the only way out is to fire. This makes it easy for the enemy to sneak up on you, because if you let go the space bar to go out of sniper mode to defend yourself the canon will fire into space, which gives freeze or fire plenty of time to kill you before you can reload. Same thing with railgun, because you may need to re-aim, but if it fires and misses the reload time will get you killed.