20 gauge shotgun shell 20 gauge shotgun shell is a type of in " " . Background . " Gauge " is used to describe the bore size of a shot - firing weapon . Although bore sizes range incrementally from 1 . 5 up to 32 ( with an aberrant 67 . 5 topping the scale ) , 10 , 12 , and 20 gauge ( aside from the . 410 shotgun that measures in caliber ) are the most common bore sizes , with 12 gauge leading the group in popularity . A 20 gauge shotgun has a bore size of 15 . 6mm ( . 62 " , or 62 caliber ) , where the gauge number is the number of lead balls of that gun ' s bore diameter that would weigh a pound . Sizes of shot is the individual lead or steel pellets that are fired from the weapon , which vary as well . A typical 20 gauge shotgun shell loaded with # 3 buckshot contains eighteen to twenty pellets . Each pellet is 6 . 35 mm in diameter ( 0 . 25 " or 25 caliber ) and weighs 1 . 52 grams . Characteristics . Masterson low recoil / max power 20 gauge shotgun shells are very similar to their larger , better known cousins , . Smaller in bore size , they have lighter powder loads and a smaller amount of shot , resulting in lower recoil and reduced target effect . 20 gauge shotshells consist of a plastic hull loaded with pistol powder and using multiple projectiles or a single slug . Production . Standard buckshot , magnum buckshot , 3 / 0 magnum buckshot and slug 20 gauge shotshell can be crafted at a reloading bench . A single shell requires the following ingredients : Breakdown . Breaking down a standard 20 gauge shotshell yields : Variants . 20 gauge , magnum . Magnum shells are standard buckshot shells fitted with a higher internal powder load , increasing velocity and stopping power . The downside is that they cause more damage to the firearm used due to the higher overall pressure , requiring more regular maintenance . 20 gauge , slug . Slugs contain a large lead projectile promoting better accuracy and kinetic energy over a distance . Slugs enable a shotgun to engage targets at a further distance . 20 gauge , 3 / 0 buck . A sub - type added with the new add - on " Gun Runners ' Arsenal " , these loads sacrifice quantity for quality , in other words there are fewer projectiles overall but they ' re heavier and pack a bigger punch . 20 gauge , 3 / 0 buck magnum . A sub - type added with the new add - on " Gun Runners ' Arsenal " , these magnum shells use the larger 3 / 0 shot size , but with a greater powder load resulting in higher velocity . The Hand Loader perk is required to craft it . 20 gauge , pulse slug . A sub - type added with the new add - on " Gun Runners ' Arsenal " , these slugs cause more damage to power armor and robots , and the target gets an extra kick from an electromagnetic pulse triggered by the impact . Notes . 3 / 0 buck rounds only have a x1 damage multiplier yet standard 20 gauge shells have a x1 . 2 multiplier and magnum shells have x1 . 3 , including the 3 / 0 magnum shells ( these multipliers were added as part of patch 1 . 5 as an incentive to use them over slug rounds ) . As a result , 3 / 0 buck actually inflicts less damage than standard shells while inflicting more damage per projectile as damage is divided evenly among them .