Well all 4 models were available in 22lr and there were many more made than 862 in 22LR, since it was the most popular caliber for the single shots across the board. There were 862 first model 22 single shots made, if that is what you meant. The straight line possibility is out since there were only 1870 fourth model aka straight lines made, all with 10 in barrels (I suppose there could be a few special order barrel lengths) and the SN is out of range for those, 1 - 1870. In addition, the SN is out of range for a 3rd model, 4618 - 11641. So that leaves only 2 possibilities, a 1st or 2nd model single shot. In addition, 8 in barrels were available on first and second models, so it must be one of those.