A friend has an 870 that I'm buying from him. It cycles through 2 3/4, 3 and 3 1/2 shells. I want to put a cantelever scope mount barrel on it but I can't seem to find any information that will tell me which barrel to buy. I was looking at the Remington barrel but they don't have this gun listed, the same with the hastings barrel...Any thoughts?

Any of those barrels will fit on the super magnum gun, in fact, any 870 barrel will fit. The only difference is the receiver stroke whether it is 2 3/4, magnum for up to 3" shells, and the super mag up to 3 1/2". The only reason they don't list a 3 1/2" barrel is because they don't make a slug barrel with that long of a chamber, but the 3" barrels will work on the super mag, just be sure not to shoot a 3 1/2" shell thru that particular barrel. Between the hastings and remington slug barrels, I would get the hastings as it usually is the most accurate but then again they all differ. Good luck.
SuperMag

The Hastings is a good bet Max.

Max, supermagnum is right. Any 870 barrel will fit your super magnum as long as it is the same gauge. I just picked a smoothbore barrel up at the last gun show that will take 2 3/4 or 3" shells. Most everyone tells me that I don't want to shoot 3" slugs anyway. I believe the reason is that they shake your brains loose in you skull........!!
Just don't go and buy a 2 3/4" chambered barrel and fire 3" or 3 1/2" shells out of it. You may end up with a very short barrel and some serious injury.

Thanks for the information! It all makes sense to me now. I just didn't want to purchace something and either hurt myself od need to return it.