Barrels

A barrel serves to direct the paintball and control the release of the gas pocket behind it. Several different bore sizes are available, to best fit different sizes of paintball, and there are many different lengths and styles. Most modern paintball markers have barrels that screw into the front receiver, as opposed to some older types which slide a barrel on and screw it in place. Barrel threading must be matched to that of the marker. Common threads are Angel, Autococker, Impulse/Ion, Shocker, Spyder, A-5, and 98 Custom.

Barrels are manufactured in three basic configurations: one piece, two piece, and three piece. It is more common to refer to a barrel with interchangeable bores, be it two or three piece, as a barrel system, rather than a two-piece or three-piece barrel. This avoids confusion, as many two-piece barrel systems do not use an interchangeable bore system.

One piece barrels are machined from a single piece of material, usually aluminum. Paintballs can range from .669 to .695 caliber, and barrels are honed to match these diameters. Many one piece barrels have a stepped bore that increases from their rated bore size to around .70 caliber after eight inches.

Two piece barrels consist of a front and back. The back attaches to the marker and is machined with a pre-specified bore between .682 and .695 caliber. The front makes up the rest of the length of the barrel and contains the porting. Fronts usually have a larger bore than the back.

Three-piece barrels, instead of having multiple backs each with a different bore, have only a single back. A series of inserts, or sleeves, with differing bores are inserted into the back. The front is then screwed on to keep the sleeve in place. Sleeves are generally offered in either aluminum or stainless steel. This type offers the most flexibility in that the user needs only one set of sleeves and a back for each marker they own. They can also select front sections to make the barrel length they prefer. This type also generally offers the widest selection of barrel diameters, usually .680, .681, .682, .683, and so on up to .696 caliber. The sleeves are generally manufactured in stainless steel or aluminum. Aluminum inserts are generally known to dent or scratch easily, so stainless steel inserts are usually suggested.

A good example is the Smart Parts Freak barrel, which was the first product to innovate this idea. While sacrificing effective barrel length, this system allows for many bore sizes, allowing exceptional accuracy.

Length
The length of barrels can range between 3 and 21 inches, though some custom barrels exist which may reach up to 48 inches. Recent tests have suggested that neither accuracy nor efficiency can be gained in barrels beyond 8 inches long, as a paintball needs an unported 6 to 8 inches to stabilize and achieve maximum gas efficiency. Longer barrels generally make less noise than shorter barrels by allowing excess gas to escape more slowly from porting along the sides. Longer barrels can allow players to "sight in" faster than they would with shorter barrels and thus give the perception that longer barrels are more accurate. The barrel choice commonly used by players is 14-16", as it keeps the balls shooting straight, but the marker is still light and maneuverable. Many players will also choose the longer barrels as it allows them to push aside the large inflatable bunkers commonly used in paintball tournaments while still staying behind cover.

Most barrels are ported (or vented), which means that holes are drilled into the front of the barrel allowing the propellant to dissipate slowly, decreasing the sound signature of the marker. There has been a considerable amount of marketing hype surrounding barrel porting, but there appears to be no basis for claims of the benefits of porting (such as that it decreases "turbulence", increasing accuracy), other than the decrease in sound signature.

It should be noted that porting in the first eight inches of the barrel length decreases a marker's gas efficiency. For example, if a 16 inch barrel has large porting that starts six inches past the threads then it has an effective barrel length of only six inches. At that point, the ball has to travel the other 10 inches on its own momentum. The friction within the barrel must be overcome with a larger burst of gas, decreasing efficiency. Porting in a barrel before the paintball has completely stabilized can also dramatically increase noise, as the gas still has a significant amount of pressure built up.

Bore
The bore is the interior diameter of the barrel. The bore properly matching the brand of paint being fired is the most critical aspect of a barrel, far beyond gas efficiency or silence in most situations. A poor bore/paint match will result in velocity variations, which causes inaccuracy. Two and three-piece barrels allow the barrel bore to be matched to the paint diameter without entirely new barrels. Paint to barrel matching is doubly important in closed-bolt markers (as ball detents in such markers serve to prevent double-feeding, not to prevent roll-outs) such as Autocockers, because small paint in a large barrel can roll out the front of barrel.

Spin barrels
The Flatline barrel, manufactured by Tippmann is designed to decrease the parabolic travel of fired paint. The barrel is curved such that an accelerating paintball contacts the top of the barrel, imparting backspin. This backspin generates lift (known as the "Magnus Effect"), resulting in a flatter arc and longer range. This is especially beneficial in woodsball or scenario paintball where overhanging branches limit the range of traditional barrels. It is available for the Tippmann Model 98, 98 Custom, A-5, and X7. There are conversion kits to allow the use of the flatline barrels on some other guns, as well.

The Apex barrel, manufactured by Ben Tippmann Paintball Design, also imparts spin to the ball. Unlike the flatline barrel, the Apex can impart back, top, or sidespin (this allows balls to arc around some obstacles, or have them drop over bunkers). The magnitude of spin can also be varied, allowing for a gentle curve or a sudden hook. It is available with threads for most markers. There are many ways to fit an Apex tip onto a regular barrel, ranging from improvised methods such as electrical tape, to sleeves that go over the tip of the barrel, sold at Underground Mod Shop and Palmer's Pursuit Shop.

Both the Flatline and Apex barrel systems have been criticized as sacrificing force and accuracy for increased long range. Paintballs fired from these barrels are able to travel farther, but due to the backspin and consequent lower speed, the chance of the paintball breaking or even hitting its target at the increased range is diminished appreciably. Given that players are tempted to utilize the extra range of the barrel at distances where the paint will not break, the barrels' effectiveness as an elimination tool (as opposed to psychological and area denial effect tools) is questionable.