Remove the stock and compare the frame to the pics of the differences between frames in the FAQs, or call H&R and ask what it is, what barrel was on it from the factory, they'll know by the serial number. Frames aren't marked SB1 or SB2. Excess headspace can cause flattened primers, if it's out of spec, H&R may replace it. Proper handloads would make it work just fine after fireforming brass and not pushing the shoulder back when sizing.
Tim