Pete has it right. H&R is pretty particular about what frames they will hook up a high pressure barrel on. It has to be a SB2 frame and it needs to be of recent manufacture. Look in the FAQ for frame serial numbers they will hook up a new barrel. I have 2 frames with 6 rifle barrels. Both are SB2 manufactured after 2003. Again, look in the FAQ about what years they will hook up a high pressure barrel.
I also hate it when I have questions about a thing I am interested in buying and the sales person does not know as much as I do about the subject. I do a lot of shopping at the local Walmarts - but only if I know exactly what I want with out asking questions. I have found the people working there in general do not have a clue about the subject you ask. If I want electronics, and I have questions, I will not go to a Walmart, I go to specialty electronic stores where they know what they are talking about for instance. I have bought guns at Walmart, but I know exactly what I want before hand. I have also bought guns at a local gun shop, not because of price, because they know what they are talking about. Information is valuable and some times you have to pay for it.