Your SB2/.243 frame will work just fine with the 209 primer, as long as the barrel locks up on it. Not all barrels fit exact from one frame to another, and may require some minor fitting. They made Huntsman Combos a few years back on SB2 frames, and it came with the .50 cal and .243 barrels. All the rest of the Huntsmans were on SB1 frames.