Projectile launchers have an elongated cylindrical body defining a projectile bore having a bore axis, the body having an open forward exit end, the body having a gas inlet facility at an opposed rear end, a movable latch element connected to the body and having a latch portion movable between a retention position in which the latch portion protrudes into the bore and a release position, and the latch element being biased to the retention position such that a projectile in the bore rearward of the latch is retained by the latch portion except until a gas pressure above a selected amount builds up behind the projectile to overcome the biasing of the latch and launch the projectile. The latch element may be clear of the bore when in the release position.