If it's a factory fitted barrel, contact H&R toll free at (866)776-9292, and make arrangements to send it in for repair/barrel replacement, they're real good about honoring their warranty well after it's expired, whether you are the original owner or not. You can tell if it's factory fitted by the 3 digits engraved on the left side of the underlug, should match the last 3 digits of the frame serial number. If it wasn't factory fitted, please read the barrel fitting instructions in the FAQs, if you have questions, feel free to ask.
Tim
