If you are talking about barrel options other than the 223, it depends on the serial number. All the newer ones will accept any barrels made by H&R-NEF. The best thing to do is to call their customer service and give them the number so they can verify your option. Their phone number and all the info you will need is at
www.hr1871.com . Go to the barrel accessory program and check it out. I am a big fan of the NEF rifles. I have several of them and have added several barrels to some of them. The 223 is very accutate. I have had three of them. Two with the bull barrel and one with the standard barrel. I would stay away from the 243 in this rifle. I have had two of them and had extraction problems and pressure problems. All other calibers seem to be fine. They are fixing the case sticking problem with a new mechanical extractor which should once and for all, fix the sticking case problem. Some of the guys have had no problem with the 243 but some have. My favorites are the 44 Mag, 357 Mag and 45-70.