This is the SRSS-501v2. I updated it from v1 by completely re-designing the barrel, making the top open so it's easy to load, and I've made the bi-pod sturdier.
Here's a video of it:http://www.youtube.com/watch?v=9JWvQwNxn5w
UPDATE: I modified it to look and function barrel. Here's a link-http://www.instructables.com/id/SRSS-501v3/