MACHINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only ENGINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only PUMPS positive displacement rotary or oscillating piston reciprocating piston or other non-positive displacement This class covers also means for practice and training which may have aspects of simulation, e.g. in apparatus for so-called "military games", although simulators are generally covered by class . In this class, the following terms or expressions are used with the meanings indicated: "smallarm" means a firearm which is generally held with one or both hands for firing, but this term also includes a light machine-gun which may be supported on a tripod or the like during firing; "gun" means any weapon having a barrel and a trigger or firing mechanism for projecting a missile; it may be a piece of ordnance or a smallarm. It may use combustible or explosive propellant charges, air pressure, electromagnetism or other propulsive forces; "revolver-type gun" means a gun having a revolving drum magazine, the chambers of which are used successively as firing chamber; "revolver" means a revolver-type pistol; "semi-automatic firearm" means a firearm from which one shot is fired after actuation of the trigger and which then returns to a condition for firing a subsequent shot upon renewed actuation of the trigger; "automatic firearm" means a firearm which will continue firing so long as the initial firing pressure is maintained on the trigger; "sighting" means bringing into visual coincidence a direction defined by a so-called "sighting" device with the direction of a target; "aiming" means bringing a weapon to a direction differing from the sighting direction by corrections in order that the projectile may hit the target; "laying" means setting a weapon in the correct position for hitting a target. Attention is drawn to the definitions of "projectile", "missile" and "rocket" given in Note (2) following the title of class . This subclass covers those features or details which are considered to be of a kind generally applicable to, or to be concerned with intrinsic functions common to, both smallarms and ordnance. Such features or details are classified in this subclass, even if they are stated to be applied only to smallarms or only to ordnance. Attention is drawn to the definitions given in Note (2) following the title of class . KINDS OF PROPULSION BREECH MECHANISMS UNLOCKING MECHANISMS GUN RECHARGERS, EXTERNALLY POWERED GUNS FEEDING OR LOADING, MAGAZINES ASSEMBLY FEATURES, MODULAR CONCEPTS, ARTICULATED OR COLLAPSIBLE GUNS COOLING, HEATING, VENTILATING, BLOWING TROUGH EXTRACTORS, EJECTORS SAFETY ARRANGEMENTS FIRING OR TRIGGER MECHANISMS, COCKING BARRELS, GUN TUBES, MUZZLE ATTACHMENTS GUN MOUNTINGS, e.g. on vehicles Permitting recoil Permitting elevation or traversing CLEANING OR LUBRICATING TESTING ADAPTATIONS FOR TRAINING OTHER ACCESSORIES OR DETAILS SUBJECT MATTER NOT PROVIDED FOR IN OTHER GROUPS OF THIS SUBCLASS Feeding elements or concepts of general interest, not specially adapted for feeding multibarrel guns, are classified in groups or . Feeding elements or concepts of general interest, not specially adapted for feeding two or more kinds of ammunition or from two sides, are classified in groups or .