[stuckinthe60s]

so....you guys are telling me lugs don't wear out and that o&u's / sbs' don't loosen up? lol.

to the op.....you can wear out a shotgun and the area of the gun that your buddy was most likely explaining was the bbl lug or where the bbl meets the receiver. as a gun wears, the pivot lug or lock up system wears. an indicator is the release latch on top. as a bbl wears (or the bbl & lug system depending on the make of gun) the latch will slowly over time move to center of the gun. this is known as the 6 oclock. most new guns will have their latches far to the right or better known as or refered to as a 4 or 5 oclock.
most likely, that's what he meant.
wear and longevity of a bbl lug or the lock up on a gun varies from brand to brand.
skb? skb's are mostly in the top 10 of well built guns. wear it out from typical use? possible...but most likely faster if abused.
keep in mind, trap guns open and close MORE than a skeet gun. so most trap guns need to be and are built stronger. (lc smith, parker, Ithaca) some of them are 100 years old and still tight. and with minor tweeking, go another 100 years.
skb? well, if a browning or krieghoff can wear out....an skb is certainly possible.
I think your buddy was trying to say he wore out the lock up, not the actual tube the wad travels down. (figure of speech)