In gas-powered guns, added barrel length (to an appropriate extent) can result in increased velocity and accuracy to a degree. Tighter bore barrels will increase velocity because there will be less space between the pellet and the barrel for the air to escape through. Most stock airsoft guns have bore barrels, but best performance is usually seen with "tightbore" barrels, which are in diameter. However, the tighter the bore, the more likely the chance of a pellet jam, and subsequently, tightbores need to be cleaned and lubricated regularly. It is generally agreed upon that a high-quality 6.01-6.02 mm barrel will provide the highest muzzle velocity, while a good quality 6.03 mm or 6.05 mm barrel will provide the best compromise between power, accuracy and ease of maintenance. The actual accuracy difference between tightbore sizes is debatable and usually outweighed by bore consistency. Although with the new found popularity with HPA guns the debate has been opened that barrel's with a larger diameter (up to ) could provide a more accurate shot. Due to the higher volume of air surrounding the pellet it negates the chance of the pellet coming into contact with the barrel throwing the pellets trajectory off similar to a musket, in how the bullet slams about before leaving the barrel.