Rifled barrels for 870

[Edenwildfood]

What are the differences between the different length barrels for the 870. Mine has a 20" fully rifled barrel but I've seen many that have longer barrels. Is there a diff twist rate?

[Scorpion8]

Length is usually a function of use. HD barrels will be shorter, while a slug barrel is mid-length. Trap or clays barrels can be 32-34". My slug barrels are all 22-26".