From Tformers.com, New DR WU DW-P38U Megatron Transformers Classics Colors Gun Accessory Revealed (19/02/2013):

Following the DR WU DW-P38C is the DW-P38U Gun Accessory this time in the Transformers Classics colors that pay homage to Megatron's alternate gun mode in the original colors. No details on a release date yet, but we expect this guy to sell for around $8 USD like the DW-P38C did. check out the image below for the full reveal.