OK, with the first 2 letters HN it looks as if your gun was manufactured in 1999 and H&R will currently fit ALL barrels to that frame, both "low intensity" (shotgun, .223, 30-30, 45-70, etc. and "high intensity" barrels, 30-06, .270, 7mm-08, .308, .280 etc...
Most people don't disclose the entire serial number just for security reasons and if you want just go back and edit the first 3 numerals with x's. The last 3 numbers on the barrel lug match the last 3 numbers of the serial number so it appears that gun came from the factopry that way ot the barrel was factory added at a later date, both are good.
H&R's warranty is for one year but their customer service is top notch and for a safety issue like this they would fix it for free. Just call them during business hours and explain the problem and I am sure they will take care of it. Otherwise, first clean, clean, clean.....Check the area around where the barrel locks up into the reciever and the area of the ejector. Does it do it with all ammo or just a particular load/brand? Has it done it since new in 1999?.. If so has it gotten worse with time?....<><.... :grin: