Back-Check Valve
It is found in 12 gram quick changers, and is intended to create a seal when a spend twelve gram is removed. The back check valve holds a small amount of gas in the valve and is usually good for one or two shots. This was designed to give players the capability to have a shot or two, should they be caught changing twelve grams by their opponent.

Ball Flag
Another name for a ball jock.

Ball Jock
This is a type of anti-double feed device. It is a small piece of wire that has one end shaped like a triangular or rounded "flag" and the other end made in such a way as to be affixed to the outside of a marker.
The flag portion fits through a slot milled into the body of the marker and protrudes into the chamber, where it holds the paintball until the bolt moves forward to chamber the ball.

Barrel
A cylindrical tube which is essential for the guidance of the paintball and the containment of gases behind the paintball. A barrel's length, inner diameter, interior surface and general material all contribute towards accuracy.

Barrel Adaptor
This is a small collar that screws into where the marker's barrel normally goes, it allows one brand of marker to use another brand of marker's barrel. For instance a Spyder barrel adaptor can be found to alolow the user to mount Autococker barrels. The adaptor is required due to the fact that the threading on the barrels is uncompatable.

Barrel Extension
As the name implies it is a tube that fits over the end of an existing barrel to increase its length. It also increases velocity, gas efficiency and improves range and accuracy. They are popular for paintmarkers which do not have a removable barrel. They are not seen much as most markers have removable barrels, so if a longer barrel is desired, it can be purchased.

Barrel Plug
A device that, when inserted properly in the muzzle, is designed to keep a paintball within the confines of the barrel should the marker be fired accidentally. This is required use in areas where players are permitted to remove their goggles in order to minimize the potential of eye injury.

Different types of barrel plugs

Barrel Length
It is the length of the barrel measured from the chamber to the muzzle. This length does not include the chamber. Although, if you did, it would probably only add approximately three quarters of an inch in the length. This is a negligible amount and does not effect the marker's performance.

BDU(s)
Battle Dress Utilities. Military or military-style camouflage clothing.

Blow Back
1. Also known as Open Bolt (qv).

2. When many pump action markers are fired (and the shooter is not holding the pump) the bolt will blow back slightly. This reduces velocity. Some pump-action markers have return springs to hold the bolt forward on it's own.

Blow By
This is a common term used to describe any amount of extraneous gas that passes by the paintball the instant it leaves the muzzle of the barrel. This blow by will cause the ball to spin, reducing accuracy, distance or both.

Blow Forward
A semi-automatic operating system where the gas pushes the bolt forwards, chambers a ball and fires it. A spring then returns the bolt and resets the action for another shot. The blow forward design is mechanically complicated as the system relies on complex "switches" to regulate airflow and operate the system, rather than simple mechanical contrivances, like sears. The blow forward design is also more gas efficient, as there is no gas vented away to operate the action by re- cocking it.

Blue Printing
The process some airsmiths use to make the inner diameter of the barrel match the outer diameter of a particular brand of paint.

Bolt
The bolt is the part of the paintmarker whose job it is to push the paint ball into the chamber, and act as a gas seal when the marker is fired. The both can be either operated manually, as in a pump-action, or can be moved by mechanical means, as in a semi-automatic. A bolt will also have some sort of hole along it's central longitudinal axis which allows the gas to pass through, hit the paintball and send the ball out the barrel. I know of no paintmarker which does not have a bolt, in some form or another.

Bolt Knob
Usually it has a threaded end and an larger, sometimes knurled, end. The knob passes through a hole in the pump arm and screws into the bolt. This allows the bolt to move with the action of the pump. They are not permanently affixed in order to accommodate disassembly. These can also be found on some types of semi-automatic markers.

Bolt On
Used to an after market accessory that does not require drilling, machining or any requisite professionally executed modifications to the marker. As its name implies, it simply bolts on. Alaso known as drop-in.

Bore
The bore is the interior of the barrel. The bore is either in reference to the inner diameter, the inner surface, or as a general term.

Bore Drop
This refers to a paintmarker whose chamber is the same inner diameter as the barrel. The bore drop was designed to aid smoother feeding of the paintball, thus eliminating breakage.

Bottom Line
An ASA mounted at the bottom of the pistol grip or grip frame on a marker. This is to allow clearance for the goggle mask, when the tank is being used for a shoulder stock.

(L)How a bottomline mounts on. (R)A "duckbill" bottomline and mounting screws.

Bouncing Betty
See Paint Grenade

Breech
This is the area into which the ball drops in, when the bolt is in its fully reward position. The breech can be seen through the direct feed, as that is where the ball must drop from, to be loaded into the marker. The breech may be part of the upper receiver or the barrel itself.

Breech Drop
The breech drop has an area which is larger than the inner diameter of the barrel. Thus the paintball must roll up and into the chamber of the barrel from the breech. Breech drops were notorious for breaking balls as sometimes the ball was pinched between the "step up" into the barrel and the forward travelling bolt.

Bulk Feeder
See Feeder

Bulk Loader
See Feeder (qv).

Bulk Loading Tubes
See Loading Tubes

Burst Disk
This is the safety device used to prevent rupturing of the air source tank in the event of a dangerous increase in pressure. The burst disk is designed to rupture at a lower pressure level than the tolerance of the tank. Burst disks must be installed correctly. Also, over-charging the tank will, in effect, stretch the burst disk and allow the tank to be over- charged repeatedly. Burst disks should be changed AT LEAST once every playing season.
For more detailed information on Pressurized Gas Safety see Compressed Gas Safety in Durty Dan's Paintball Information Services.

Butt Plate
This term is usually reserved for a plastic or metal cap or sleeve which fits on the end of a C/A tank, thus allowing it to be more effectively used as a shoulder stock. The butt plate is usually ergonomicaly designed to better fit the shoulder, as opposed to the flat end of the tank it fits on. This term also refers to the part of a shoulder stock that fits against the shoulder.

C/A tank with butt plate

Butt Pack
See Harness.

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