Yes you do have to send them the receiver and the forend on ALL barrels. I sent my 12ga receiver & forend in and got a 20ga rifled slug barrel and a 20ga full choke. That was 10-12 years ago and for both barrels it only cost $110 for both barrels. I can only imagine what it costs now.
The H&R/NEF barrel program use to be a great deal. Not so much now since the Freedon Group bought them. Prices are rising faster than I have ever seen. The guns were a great deal as well, not anymore. I feel they are overpriced for what you get now.
Remington is who dose the work on them repairs and adds the barrels . they r somewhere in new York state. Only took them 2 days for them to install 2 new barrels and ship it out . should be here today cant what.
Google H&R1871, it will take you to their website. Go to Customer Service, then Barrel excchange program. There are some conditions you need to read, and they have a great customer service dept if you need to call with questions. Good Luck.