Suspect RememberTheSomme is right. There are a lot of daft international rules and regulations around these days. Only some of which come from the Third World Debating club.
Lot of silly internet ideas too. .308 Win and 7.62 NATO being some how different, for example. Literally millions of rounds of both have been fired out of rifles with either designation with no fuss, long before there was an Internet. Millions of round were reloaded too. So how a rifle is marked doesn't matter much, except to the assorted countries frightened of rifles in the hands of their population.
I believe 'Socom' is an SA Inc. trade mark for their fantasy M1A carbine. No such thing as a 18ish inch M-14.