How can I tell if I have a 1st gen or NS2 (2nd Gen) version of the KWA M11A1?

The bolts on the original M11A1 and the current NS2 version are nearly identical. The easiest way to tell which version you are looking at is to look at the cut in the bolt, although a metal-tipped (rather than the current polymer) cylinder will also let you know that you have a 1st gen version.