Commonwealth Walker has the same HP and damage as the Armored Walker, and is also bulletproof. Being bulletproof means there is a very high chance your ranged attacks towards them will result in a Bodyshot. In addition to this, the walker is resistant to all status effects, but that resistance drops in quartiles as their HP drops. The 4 red dots on top of the walker indicate their current status effect resistance. In short:

100-75% HP = 100% Status effect resistance - 4 red dots
75-50% HP = 75% Status effect resistance - 3 red dots
50-25% HP = 50% Status effect resistance - 2 red dots
25-0% HP = 25% Status effect resistance - 1 red dot