All factory 357 and 44 mag rifles made 2008 and later are on SB1 frames, those made prior to that were on SB2 frames, barrels are marked SB2 which doesn't mean anything as to the frame they come on, it's just misleading, there are a bazillion posts here on the subject. Read the statement on the right side of those SB1 rifles, it makes it easy to tell if it's an SB1 or not. Doesn't really apply to accessory barrel fitted frames since H&R has been fitting those barrels to SB1 frames since late 2008 which won't be marked.
Tim