The BM stands for "big mother."
"Could you please explain to me what this is and what it's used for?
What your question means to me is you know nothing about guns, so the survey you fill out will be filled with ignorance on other things, not just the .50
If you were interested in guns, you would not come here to ask, you would know where the dedicated source sites are on the web.
I get junk surveys every day on subjects I know or care nothing about, they are filed under W immediatly. Why don't you do the same in this instance, don't give input on matters you know nothing of.
It's nice of everyone to help the lady out, but can't someone post some really cool gun porn for this Friday nite?