SPOILERS: The final episode with the machine gun.
SPOILER ALERT.
In the final episode Walter manages to kill all the Nazi biker gang (well almost) using the automatic setup with the Bren gun (or whatever it was) in his car. This was a major gamble - how did he know, for example, that the gang would be in a ground floor room and all within the limited range of the gun? How did he know he would be able to park his car within range and pointing in the right direction? I guess perhaps he didn't care too much as by then, he'd achieved his main goal which was to ensure his money was safe and he had no other real alternatives to get rid of the gang.