BAMs, or Biped Artillery Mechs, are the riflemen of the Golden Bolt. The two massive cannons mounted on their backs are used for taking out far away targets. With some training, the pilot can nail targets nearly a half-mile away.
B.A.M.s are mostly used to back up other mechs, tanks and infantry. They fire both Anti-Tank and Anti-Building rounds that can obliverate most heavily armored tanks and bunkers.
Coincidentally, I was reading a Warhammer 40K Tau Codex and found a mech that looked remarkably similar to my B.A.M. called the Broadside Battlesuit. The similarity is uncanny, and I had never even heard of the Tau when I constructed this model.
I do beleive that artillery and sniping are two opposite things. You said that it was used for sniping out targets, but artillery is usually used for wide-spread damage. Well, I guess it would be possible, but artillery/sniping just don't seem to go well together for me. But it's your MOC, do what you want with it.