Thanks for the stars everyone. I actually did some testing with most of the game's infantry and i'll post that later when i get the home. Though you're right about the gunner as it is the best infantry at taking down buildings given its range and overall damage.Anyway, here's a good tatic for Mesa. At around 400 credits try and organize a group of 4-5 gunners. Have your group take the path down the barricaded side of the base until you reach Nod's barricaded side overlooking their refinery. Once all your gunners are in position, start pounding away on the refinery. I beleive that 5 gunners took about 2 reloads to bring down the building.