This guy was part number 010120501 and had the weapon options of a bolter arm (010119902), a storm bolter (010110302) or a combi-melta-bolter (010120502). This guy came with the latter.
1999 as the sculpt date on the back, and either nothing on the front or it was filed off by a previous owner. No idea who sculpted him – the catalogues I have found showing this miniature don’t state. He looks very Black Templars-y – may end up not doing him as an Ultramarine.