Based on the Megatron Origins version of Sentinel Prime. Just a repaint of a KO oversized Suppressor/Firebolt/Buckshot minicon.
I like the alt mode, and the robot head (I had to paint the eyes), but I'm not convinced I've got the robot colours OK. For some reason it reminds me of a Jack Kirby design.
http://i48.tinypic.com/axxv0h.jpg
http://i46.tinypic.com/25570ps.jpg
http://i50.tinypic.com/2it21bs.jpg
http://i50.tinypic.com/2h5i7tl.jpg
