I can't remember this old action film j used to watch as a kid about 12 years ago. I vaguely remember a group of people are trying to kill this evil guy who's got this almost inpenatrable armour on which they can't destroy. I think it's set in a kind of desert and I remember they all have walkie talkie headsets and huge gattling guns throughout the film.. Any ideas? :)

Well this might sound goofy, but Robotech came to mind when you said that (probably because of all the "mech" stuff you mentioned).

I hope this helps.