The Pardner shotgun frame is color case treated as well as the Buffalo Classic, but the shotgun frame is an SB1 frame, the BC is an SB2 frame. The flat black frames are usually Sportster rimfire frames. The blued frames can probably be either SBI or SB2 depending on when it was made and for what model it was originally made. For instance the 22 mag Ultra has a blued frame but it's an SB1 rimfire frame. These are general guidelines, I'm sure there are exceptions. The best way of knowing what frame you have is to check with H&R, they will tell you what barrels can be fitted by the serial number.