12 grams offer a more compact air source and are often used on pump guns, pistols and are often preferred when playing stock class paintball.
12 grams should not be used on electronic guns, and higher end Mechs.
For 12 gram changers there are three basic styles (and most share the same seals and pierce assembly with modern CCI changers):
*Bucket Changers=a 12 gram changer which you would drop your 12 gram into a bottom "bucket" and then screw that onto the piercing bottom threads with asa top threads. Most common bucket changers are CCI, Rat Attack (Carter/Taso), and ACI/Brass Eagle.
*Drop Out ChangersThese are also very common and pretty popular. They are a long tube with a cut out and a threaded knob on the end. Drop your 12 gram into the cut out and then screw the knob in. This pushes the 12 gram into the piercer and airs up the gun. The Brass Eagle/ACI style drop outs are common and decent quality. The old school AGS/Taso are also good quality and rebuildable.
*Lever changers/Pump ChangersLine SI, AGD, ACI, NSG and others made lever changers and WGP made pump changers. Not as reliable of a pierce but usually good quality. Also not as safe to use.They look good on wall hangers but I don't usually like to use them. Parts are harder (or in some cases impossible) to find but they definitely have style.