n3twrkm4n: It's been awhile since I have looked at this, but I believe it works like this: For longguns, most any longgun legal anywhere else is legal in MA. For handguns, however, there are published regulatory standards for the firearms construction to meet certification. The state attorney general's office doesn't bear the burden of testing compliance. Rather, that must be done by the manufacturer, using an independent lab, and the results of testing submitted to the state.
Not all handguns made would pass, but most of them would, if they were run through the process. Smith & Wesson, Ruger, Beretta, SigArms, Kahr Arms, Walther and Para Ordnance have gotten many of their handguns certified (I'd guess at least 200 handguns on the current approved list). But Colt and Springfield haven't bothered to even try. Glock came within a whisker a few months ago, but there turned out to be some snag... I am still hoping that Glock will make the effort to see it through.