Wait wait wait, it looks like at least the UK, France and Netherlands use not the standard Minimi but the shorter Para version (349mm-long barrel instead of 465mm, from
world.guns.ru and Herstal).
I don't know exactly how MGs are modelled in the game, but I'd guess this version should have slightly lower range and accuracy.
Check the official pages for confirmation (pics with stubby barrel and folding stock and max length of 0.914m instead of 1.040:
Minimi in the UK
Minimi in France
Minimi in the Netherlands
AFAIK the M249 is similar to the "standard" variant, so users of the 'long' version should be at least USA, USMC, Canada, Belgium, Italy.
I'll try to find more info on who uses what exactly, if that can help standardize the versions.