Since the advent of semi-automatic markers in the early 1990s, both insurance and competitive rules have specified that markers used in paintball must be semi-auto only; specifically, that only one paintball may be fired per trigger pull. While this was a perfectly clear definition when markers were all based on mechanical/pneumatic designs, the introduction of electronically controlled markers in the late 1990s brought technology beyond the rule. Electronic markers are often controlled by a programmable microcontroller, on which any software might be installed, including software that may add more than one shot per trigger pull in various ways. This effect is generally referred to as "shot ramping" (as opposed to velocity ramping): an electronic firing mode where a consistent full-automatic rate-of-fire will be triggered as long as the player maintains a certain, lower trigger-pulls-per-second.
Pump action
Pump action markers must be manually re-cocked after every shot, much like a shotgun. This manual action is slower than other configurations, but is preferred by some over semi-automatic markers as a challenge to themselves to learn how to play with less rate of fire. Others merely cite the increased satisfaction of playing with a pump. The slower pace of play also forces pump players to make every shot count, leading many to believe that the markers themselves are more accurate, which is partly true, because they do not have the recoil of a Semi-Auto.
Semi-auto
Semi-auto markers use a variety of designs to automatically cycle a bolt and load a new paintball into the chamber with each trigger pull. This frees the player from manually pumping the marker, allowing them to increase their rate-of-fire.
Full-auto
Full-auto markers continually fire as long as the trigger is held down. The Tippmann SMG 60 was the first fully-automatic paintball marker. Most electric paintball guns feature this mode, but the full auto feature can be added to any electric gun by buying a different logic board or a replacement electronic trigger.
Burst
Burst mode allows multiple shots to be fired per trigger pull. Two and three shot burst modes are common, and some guns have a programmable mode where the user can select the number of paintballs to be fired. Note that burst firing often leads to an effective fully automatic paintball marker when used by a player with quick fingers.
Ramping
Ramping is a feature in some electronic markers that automatically shifts the mode of fire from semi-automatic to fully automatic as long as the trigger is pulled at a specified rate. Ramping can be difficult to detect, both because it may not be consistent or easily observable by a human. Ramping modes can also be hidden in the software, such that a marker will fire in legal semi-auto mode when being tested, but in an illegal ramping mode by the player. To counter the problems with enforcing semi-auto rules, some leagues have begun allowing a specific ramping mode. The rule specifies a minimum time between shots of 66 milliseconds (approx. 15 shots per second), and that no more than one shot may be fired for the first three trigger pulls. The rate of fire is enforced using a device called a PACT Timer, a standard firearms timing device that measures the time between shots.