Barrett "Light Fifty" rifle

[piper4]

Hi

Could any one tell me how the Barrett got the "Light Fifty" tag, and how would you transport one of them about?

The reason I am asking I write stories as a hobby and am trying to make it as realistic as poss, I normally write westerns so this is a real departure for me, and this particular rifle fits into the era I'm writing around.

Thanks so much

Piper4