One, knuckle duster is a prohibited weapon under Tennessee's
going armed statute and would not gain you any brownie points
against a victim defending herself with a pistol with a legal permit.
That said, the victim-defender would still probably be charged with
voluntary manslaughter, which would usually not be adjudicated
until at least the grand jury level.
How the heck the FBI shows ~170 justifiable homicides per year
from uniform crine reports (which do not reflect adjudication) is
a mystery. Gary Kleck estimated under 3,000 justifiable homicides
by shooting after adjudication. Marvin Wolfgang wrote that when
where such statistics were kept, 20 to 30 percent were eventually
adjudicated justifiable.
Most US justifiable homicides appear to be charged initially as
voluntary manslaughter.