Malphas is correct, it is a VP70 grip. It could be from the dart, or cap pistol versions they made back in the 80s. I also remember seeing a cheap airsoft version on the Hobbytron site a while back.
I believe the VP70 with the burst fire that accepts the stock was molded with the finger grooves. Could be wrong, HK is out of my price range. But the trigger definitely doesn't look right. Looks trimmed down or something if it is the VP.
EDIT* Looking at it the mag release isn't there and the pin at the bottom isn't there either. Might be a cheap cast or probably something else.