Thanks all for your informative replies on drum magazines.
I have seen a few pictures of the RPK-16 (prototype model perhaps) with a drum magazine housing 95 rounds, 45-round box magazines or more standard 30 round magazines as well. However technically I suppose this is classed more as a light machine gun rather than an assault rifle - designed to replace the RPK-74 series of weapons.
The Swedish also came up with their CBJ-MS personal defence weapon which has, as an option, a 100 round drum. Very impressive for such a small firearm! Should it ever actually enter up being purchased and deployed by anyone, it would be most interesting to see if anyone used the drum or stuck with its standard 20 and 30 round magazines instead.