Marker body

The marker body is where most of the marker's functional and aesthetic features are contained. Most marker bodies are constructed from aluminum to reduce the marker's weight, and feature custom milling and color anodizing. In terms of function, the body contains the main components of the firing mechanism: the trigger frame, bolt, and valve.

External design
The largest external and ergonomic difference in marker bodies is trigger and barrel position. High-end marker designers work to push the trigger frame forward toward the center, or slightly forward of center of the body on speedball-oriented markers. This allows the HPA tank to be mounted in a position that provides compactness and balance without requiring any additional modifications that drop the tank down and forward. (Such aftermarket "drop forwards," may create a larger gun profile, which can result in eliminations due to hopper hits.) In economy markers, users often modify the marker to produce the same feel, albeit by sacrificing a low profile. Though this is an irrelevant consideration in games where equipment hits do not count, a majority of fields, including those focused on woodsball games, count hopper hits as an elimination. However, some markers mount the barrel farther back in the gun body to preserve overall compactness in lieu of positioning the trigger forward on the marker body.

Trigger frame
Triggers are one of the most important functional features, as they are the the player's primary means of interaction with the marker. The amount of force required to fire the marker, as well as the distance the trigger travels before actuating (the "throw") has a major effect on the player's ability to achieve high rates of fire. Higher-end markers employ electronic trigger frames with a variety of sensing methods (microswitches, hall effect sensors, or break-beam infra-red switches). These triggers feature very short throws, which allows for higher rates of fire. Non-electronic markers may alternatively use carefully set pneumatics to achieve a light and short trigger pull.

The trigger frame on non-electronic mechanical markers simply use a series of springs and levers to drop a sear, which allows the hammer in the body to propel forward. On electronic markers, the trigger frame houses the electronics that control the solenoid, as well as other features on the marker such as ball detection systems. Upgraded circuit boards are available to improve various features in the marker.

Bolt and valve assembly
The bolt and valve assembly is the core of any marker. Together, they provide the mechanism by which the marker fires. The valve is the mechanical "switch" that controls whether the marker is firing or at rest, while the bolt directs the flow of air and controls the entry of paintballs into the chamber. The bolt and valve may be separate components (as is the case in many blowback and poppet-based electropneumatic markers), or the valve may be "built into" the bolt (as is the case in spool-valve electropneumatic markers).

The majority of markers on the market today are open bolt, which means that when the marker is at rest, the bolt is in the "back" position, and the firing chamber is exposed to the stack of paintballs being fed by the loader. Some markers, however, are closed bolt, meaning that in the rest position, the bolt (and paintball to be fired) are forward, and the feed stack is shut off from the chamber. It was once believed that closed bolt markers were more accurate due to the absence of a reciprocating mass when the marker was fired, but tests have shown that the position of the bolt has little effect on a marker’s accuracy.

Bolt and valve in mechanical markers
The majority of mechanical markers employ a simple blowback design utilizing a poppet valve (also known as a “pin valve”), which is opened when struck by a compression force, provided in the form of a hammer propelled by a spring. These sorts of markers generally use a “stacked tube” design, in which the valve and hammer is contained in the lower tube, while the bolt, which is connected to the hammer, is in the upper tube (Some manufacturers, however, such as Tippmann, have managed to incorporate the valve, hammer, and bolt into a single tube, as exemplified in the Tippmann 98 Custom). The hammer is held in the back position, with the spring compressed, by a sear. When the trigger is pulled, the hammer is propelled forward by the spring, into the valve. The air released by the valve is then simultaneously channeled up to the bolt to fire the paintball, and back to push the hammer back into the cocked position (hence the name “blowback”).

Poppet valves are usually easy to replace and require little, if any, maintenance. The downside to this design, however, is its high operating pressure, which leads to a larger recoil and arguably less accuracy. Some markers, such as the Autococker, have a separate firing and recocking sequence, which decreases the recoil caused by the cycling of the hammer. Any marker with a hammer, however, has a significant firing delay when compared to a full electropneumatic.

Some markers are a hybrid of mechanical and electronic features. In these markers, the hammer and spring continues to activate the valve, but the hammer is released by a solenoid in an electronic trigger frame.

Bolt and valve in electropneumatic markers
Whereas mechanical markers use a spring and hammer to actuate the valve and cycle the bolt assembly, electropneumatic markers rely entirely on the rerouting of air to different locations in the marker. This rerouting is controlled by an electronic solenoid activated by the trigger. There are two broad categories of bolt/valve mechanisms within electropneumatic markers: poppet-valve-based and spool-valve-based.

Poppet-valve-based electropneumatic markers are very similar to mechanical blowback markers in that they feature a stacked-tube construction, built around a poppet valve, that is opened when struck by a force. However, unlike mechanical markers which provide that force with a hammer propelled by a spring, the valve in poppet-valve electropneumatic markers are activated by a pneumatic ram. In the same way that the bolt is connected to the hammer in mechanical blowbacks, the bolt in poppet-based electropneumatics is connected to the ram. Poppet-valve electropneumatics share the same disadvantages as their mechanical counterparts, namely external moving parts, a reciprocating mass, and a louder firing signature. However, they are also more gas efficient than spool-valve electropneumatics since the poppet valve only releases the precise amount of air needed to fire the marker. Examples of markers that utilize this mechanism are the WDP Angel, Planet Eclipse Ego, Bob Long Intimidator, and Bushmaster.
In a Spool-valve-based electropneumatic marker, the bolt also acts as the valve. This eliminates the need for a stacked tube construction, and indeed spool valve markers are notable for their compact profile. Rather than employ a cycling hammer or ram that strikes a pin valve, the movement of the bolt is controlled entirely by the routing of air into small chambers in front of or behind the bolt. Additionally, there is an air reservoir behind the bolt that contains the air that will be used to fire the paintball. When the marker is at rest, air is routed to the front of the bolt to prevent any of the air in the reservoir from escaping. When the trigger is pulled, that air is either vented, allowing the air in the reservoir behind the bolt to simply push it forward (as is the case in an “imbalanced spool valve” design), or the air is rerouted to a small chamber behind the bolt (separate from the reservoir), which then pushes the bolt forward (a “balanced spool valve” design). In either case, the movement of the bolt forward exposes pathways in the bolt or the marker that allow the air in the reservoir behind the bolt to surge forward and fire the paintball.

A typical spool valve has at least one O-ring that undergoes a shear/compression duty cycle every shot, leading to faster wear and less reliability. Additionally, the necessity of an air reservoir makes them less gas efficient than their poppet-valve counterparts. However, since spool-valve markers feature no reciprocating mass (other than the bolt) and require little pressure to operate, they have less recoil and very little noise. Examples of markers that utilize this mechanism are the Dye Matrix, Smart Parts Shocker, and Smart Parts Ion.

Tuning the bolt and valve system
In mechanical and poppet-based electropneumatic markers, the valve is usually designed with a specific operating pressure in mind. Low pressure valves provide quieter operation, and increased gas efficiency when tuned properly. However, excessively low pressure can decrease gas efficiency as dramatically as excessively high pressure.

Additionally, the valve must be set such that it releases enough air to fire the paintball. A valve that is not tuned properly can cause an insufficient amount of air to reach the bolt. This phenomenon, known as “shoot-down,” causes fired paintballs to gradually lose range, and can also occur at high rates of fire. Some markers have integral or external chambers, called low-pressure chambers, which hold a large volume of gas behind the valve as a means of solving shoot-down.

Due to the open bolt design of most markers, the bolt movement when a marker is fired can cause some air to blow up the feed tube and disrupt the feeding of paintballs into the marker. Proper tuning and choice of loader can solve this, however.