I suspect that "killing of a felon in commission of a felony" is part of the FBI instructions to police on when to use the UCR code for justifiable homicide in police reports on homicides. Vague descriptions can lead to vague police reports.
For what this example is worth: the Sanford PD incident report on the shooting of Trayvon Martin by George Zimmerman lists the offense as being investigated as "Homicide -- Negligent Manslaughter -- unnecessary killing to prevent unlawful act" with UCR code 090C. I suspect a lot of adjudicated self defense killings are investigated initially as suspected manslaughter (as are a lot of adjudicated murders).
An anti-gun type could have a field day in comparing the murders (~13,000) to the justifiable homicides (~400)
Which would not impress me much.
Gun control is more likely to affect armed self-defense than it is to affect criminal homicide.
Murder in the United States - 2011:
12,664 Total, 8,583 Firearm related.
FBI UCR Table 15 Justifiable homicide, private citizen 2011:
310 Total, 258 Total firearms.
Table 15 relies on police homicide reports using a UCR code for justifiable homicide. It is a vast under-report because homicide is usually adjudicated much higher in the justice system than the police report level. Gary Kleck has estimated FBI UCR under-reporting of justifiable homicide by a factor of 4 to 7.
One thing about murder (criminal homicide) in the US pointed out by everyone from Marvin Wolfgang in the 1950s to Gary Kleck in the 1990s: most cases are not simply ordinary people killed just because there was a gun around to "cause" the killing.
Wolfgang's sample of all murders in Philadelphia over a four year period showed many followed a history of violence and in about a fourth of the murders the "victim" initiated violence in the encounter that led to his/her demise. "Material subsequently reported in the present study regarding the place where the homicide occurred, relationship between victim and offender, motives and other factors suggest that many situations, events and personalities that converge in particular ways and that result in homicide do not depend primarily on the presence or absence of firearms.... More than the availability of a shooting weapon is involved in [gun] homicide." (And Marvin Wolfgang opened an article once with the bald statement "I hate guns.")
More recently Baltimore reported that 91% of murder victims had criminal records. In cities like Boston, murderers and their victims frequently have something in common: prior arrest for drug violations. Most murderers and their victims are part of subcultures that routinely live and settle disputes outside the legal system.
Surveys of the general US population show most ordinary gun owners (about 60%) acquire guns from licensed dealers and a minority are non-dealer acquisitions (gifts, inheritance, private sales of used guns, swaps and trades).
Surveys of prison inmates conducted and published by US Department of Justice DOJ, National Institute of Justice NIJ and Bureau of Justice Statistics BJS spanning over the decades show a majority of acquisition of guns by criminals (fairly consistently around 85%) are from non-dealer sources, including from theft, burglary, illegal drug dealers, fences who deal in stolen goods, family and friends of inmates who are often part of criminal subcultures themselves. Over the years retail sources for inmate firearms were cited around 15% (frequently using a straw buyer with no criminal record).
More gun control (in addition to legal restrictions on legal manufacture, import, wholesale distribution and retail sales already imposed by the 1938 Federal Firearms Act that created the FFL, 1968 Gun Control Act that added the Form 4473 and 1993 Brady Law with waiting period replaced by instant check) is less likely to impact the illegal supply of guns to persons inclined to violence and more likely to impact the legal supply of guns to the lawabiding citizenry.
In fact, given the history of alcohol and marijauna prohibition, the result of drastic restrictions could be acceptance of the criminal market by otherwise lawabiding citizens, resulting in loss of any legal control.