[meadsjn]

Another simple possibility is that the shooters are loading either 5.54 or .223 slugs into a 7.62x39 casing as a sabot (just as it would work for a .308 or .30-06). This way several different shooters using AK/SKS-47 rifles would be producing ballistically identical slugs (with no rifling grooves).

[TC Rider]

Another simple possibility is that the shooters are loading either 5.54 or .223 slugs into a 7.62x39 casing as a sabot (just as it would work for a .308 or .30-06). This way several different shooters using AK/SKS-47 rifles would be producing ballistically identical slugs (with no rifling grooves).

I say go for the simpler solution. These AK-74 do turn up as surplus here, along with tons of the russian ammo. I recall seeing plenty of both at recent gun shows.