AFAIK, the pre-1942 Sportsman 199, the Ultra Sportsman, and the New Defender were the only single-action, 9-shot .22 top-break H&R's, with all subsequent Sportsman, 999 Engraved, and 999 Sportsman being double-action.
MQP, Is your "single-action Model 999" marked as a Model 999 ?
If so, did you purchase it "new" ? - because if not, it might have been modified to shoot only SA, for target work, something done every once in awhile to Colt & S&W DA target revolvers, back in the 1950's (IIRC).
Last edited by PetahW; October 4, 2012 at 03:54 PM.