Welcome!! Read the Handi Basics 101 sticky and the Pop Open medicine link in the FAQs and Help sticky.
FWIW, H&R doesn't make a 20" heavy barrel 223, they make a 20" Superlight, 22" standard contour(some mistake it for a heavy barrel) and a 22" bull barrel, as well as a 24" bull and fluted, so yours has been cut short by someone if it is indeed just 20" long and a heavy contour. Barrels are measured full length, end to end.
Tim