It is a one shot with higher impact rifles if they are running max armour. If you want to run lower impact then head and then body and they are done.
Splash damage on the hammer i didn't feel was an issue, it certainly isn't like a nova bomb so i would be willing to say it could be toned down if it is really an issue.
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Try dodging a hammer yourself. It's almost impossible. They also can home in on targets, if the perk is taken.