I really don't know much about guns but yes, I do remember in TF1 them mentioning what kind of ammo worked on Scorponok. But wasn't that ammo coming from an airplane? And could soldiers on the floor carry/use guns that take advantage of that type of ammo?
But they weren't completely "weaksauce". Even with their regular guns they showed briefly how they trained to take down the 'Cons. It was about efficiency. And it worked a little.
Still, they wouldn't have won a single battle without the Autobots, and really without Optimus.