CSW_* constants are weapon indexes. What cs_get_weapon_burst() expects is a weapon entity index, just as Arkshine said. Just like players have their entity indexes from 1 to 32, all other entities (including weapons) have them, and that's what you need.
And that "weapon_*" is just a classname by which entities are recognized and linked to C++ classes.
I actually copy-pasted this into a text file for safe keeping. Thank you! That was most informative. More bacon to go 'round!...