I'll guess it's the Legacy if it's multi pump. AirMaster and 2100 are the same, and the Legacy kind of looks like the 2100 receiver.
Found a pic of it...and added to my response.
I'll guess it's the Legacy if it's multi pump. AirMaster and 2100 are the same, and the Legacy kind of looks like the 2100 receiver.http://www.crosman.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/c/l/clgy1000kt_00.jpeg