Someone asked me what the differences are between the older BM-99 and the newer 841 bases.
The BM-99 is a steel base that has a nicely polished blued finish.
The 841 is an alloy base that has a matte dark gray, not quite black, finish.
The BM-99 base is aesthetically more pleasing, more in sync with a blued and walnut rifles, and is (IMO) the best looking base for use with Weaver-style rings on a 99.