The simple term of "jams" is not very helpful. Does it jam while feeding a round into the chamber? Does it jam while extracting or ejecting the spent casing? Is it jamming on the 1st round, last round only? Is it only jamming with one particular magazine? When was the last time the magazine springs were changed? Do you properly clean, lube, and maintain these guns?
There's a number of different things to check depending on exactly how the firearm(s) jam.
Are you a new shooter or experienced? Are you shooting at a club, or range where someone else can try the gun and try to replicate the problems?