A firearm for discharging a high velocity projectile in which, to prevent injury to a firer from high pressure gases produced by an explosion in the fining chamber, a high pressure relief device is provided, which in normal use remains intact and permits normal firing of the projectile but in the event of an explosion in the firing chamber, high pressure gases which are produced rupture the high pressure relief device and vent the high pressure gases, in a direction away from the firer.