Deep Recon (Executioner Series #379) by Don Pendleton
Tensions are on the rise after a BATF agent's cover is blown during a gunrunning bust in the Florida Keys. There's a leak within the Feds, and Mack Bolan is sent in to search and destroy before more lives are lost. But with highly trained ex-marines running the guns and dedicated to eliminating loose ends, Bolan knows infiltrating the unit could be a fatal assignment.
With nothing to lose, the mercenaries are ready to declare war on whoever gets in their way. It's kill or be killed, and the Executioner is ready to take them up on their offer if that's what will break the chain of command.