Saanga grimaced as he felt multiple bullets pinging off his armor, taking small chunks of it with them. He had no choice but to leave the front of his armor half done in order to instead focus on the back enough to heal the larger bullet but he didn't care about the smaller chips for now. He'd leave those alone and instead have the rest of his focus on creating a circular shield out of the material from his palms, resulting in a 3 foot radius with a place to grasp it in the middle with room for both hands as they grasped on. He slowed down his pace during all of this to intentionally allow the mech to gain on him, and then once the shield was complete in three seconds time and the mech fired his larger weapon again, he'd leave the damage to his back as is and swirl around and rush back to the mech as fast as he could, holding the shield up to protect him from the bullets where his chest armor couldn't. 

He'd have three seconds until he'd worry about the larger gun again so could easily withstand the small arms fire long enough for him to close the 100 feet or so between them in a little over three seconds. His shield would get hit once by that weapon but it should be able to hold one of those shots. If he managed to reach the mech as planned then he'd go all Captain America on it and smash at joints he could reach with the edge of the shield, hopefully disabling it and bringing it down to his level where he could begin smashing other things.

...hopefully the mech wouldn't simply overpower him once he reached it...