You know, Azelle likes the shadows.
I wouldn't imagine there'd be any handgun calibers that could do a number on even light armored vehicles, there are specially designed AP rounds for some small calibers that are capable of penetrating kevlar plates but not full steel meant for vehicles.
Most likely would be something like the Thompson Contender G2 which is a very borderline handgun that uses rifle caliber cartridges.
HTI rifles are your best bet if you don't want something like a rocket launcher. My favourite would be the Desert Tactical HTI rifle which is the bigger brother of their Desert Tactical SRS, a bullpup, multicalibre, bolt action rifle. Lightweight and quick to set up, its a rifle that's on my armory bucket list.