There were just too many heavily armed guys all in body armor and helmets.
There were also cops in reserve away from the house, and he'd needed to get them as well, and that'd take more mines.
I'm not sure you can handle 20 cops and their vehicles with an M60 machinegun ~ again, area weapons would be needed to pull off an effective defense without getting hurt yourself.
Remember, he did not fire. Some cop fired first, and second, and third, and......
Yes, I know. I would not have fired either....