Need a read on MGL's re: post-ban stuff

Hey, I need a read from MA-smart guys on MGL's pertaining to post-ban (i.e. non-ban-compliant) mags and guns, as they relate to non-residents. To wit: it has been my understanding that MGL's make no allowance for possession or use of post-ban hi-cap mags or "assault weapons" by non-residents. That is, I can't come down to shoot a match, say, in MA with my non-ban-compliant AR-15 and my stash of PMags. This is the way I read the laws, that seems to be what I've read here, and I've always acted accordingly.

On another forum, a member is trying to organize a Tactical Carbine course to be taught by Magpul Dynamics. In discussing the options for various SoNH ranges, the discussion turned to MA, and the problems with hi-caps, etc, discussed above. One of the members from MA piped up with this:

Not true. If you are a non-MA resident, you can bring your firearms legal in your state, including non-pre-ban full-cap mags, as long as they are in a locked case, for training on an organized range. I know, right now, I'm stuck in MA, and we have Bruce Gray and Jerry Jones coming to instruct a tactical pistol and tactical carbine class May 1, 2 and 3 at my home club. As long as the firearms are kept in a locked case when not on the range, there is no need for any MA license, either.

Now, I know that they couldn't say it on the InterWeb if it wasn't true, but this runs counter to my understanding. Does this pass the smell test? Is this guy correct? Can I bring my non-compliant goodies into the MA, locked up, for training on an organized range? Is there a MGL cite that applies?

Thanks for the help.

BTW, if this shapes up, I'll make sure we get the details posted on NES.

Thanks.