User blog comment:TheAmazingBBP/OED-WY signups/@comment-1895461-20110127222134/@comment-24476373-20110127230031

It shows the power of the weapon. Some people may prefer an M240 to an M249 because one fires bigger bullets. (Not saying either of these weapons are available.)

And these weapons are made up. that's the whole point the only real ones are the M2010 and the M25, but they are both in the experimental stage and are known as the XM2010 and the XM25. (Kinda like if the XM8 was put into service, it would be the M8.)