First of all Jeff H&R/NEF will fit the new barrel to your receiver not the other way around or your excisting barrel would no longer fit your receiver. As for part 2 of your question... Yes, many folks have bought 2nd hand barrels for use on their receivers. Not to get overly malo-dramatic but this does involve some risks. If you don't know how to check for proper lock up and head spacing or don't have a competentnd gun smith check this for you, you could end up with dangerousus condition. Sometimes material will need to be removed or added to the barrel lug for proper fit, other times you get lucky and nothing will need to be done at all.
In my case I don't have enough knowledge & patience or the proper tools to check for and correct an ill fitting barrel so I would have to pay a smith to do this for me. That being the case I would rather get a new, warranted barrel, fitted at the factory than to take a chance on a used barrel. But that's me, you have to make your own call. [/b]