The 44 Russian butt-frame is almost identical to the K frame round-butt frame. The only difference is that the front toe on the 44 is square, but rounded on the Model 1899. The factory made very few target stocks for the Models 1899 & 1902, but yours could be factory, since there were at least two styles made. Yours could have been a third????
Your stocks have the concave top rounds, fine early K frame checkering, with diamonds, but without the two screw design of other stocks. The K frame target stocks I have seen were a very similar shape, and some had a extension on the upper rear of the stocks. There were at least two sets of these early target stocks. First are as a prior post by Mike Priwer with checkering pattern like the NM3, with the rear extension. Second, was checkering as Mike's show, but without rear extension, but I have no pictures of those. Late 44 DAs were sold overlapping with early K frames in those early years and could have seen more patterns. If you have not done so, maybe get a letter??