Since 1968, at least 1.4 million Americans have been killed by guns—more than all the U.S.'s accumulated war dead in that same period. Any way you look at it, 2013 was another killer year for arms manufacturers and armed bullies.

There is much debate over how to define a "mass shooting." The FBI classifies a mass murder as four fatalities, not including the killer. Mother Jones uses that, plus several situational criteria, for a mass shooting. The Redditors at "Guns Are Cool" considers any time four people are shot (not killed) a mass shooting, and with good reason: "The most obscene incidents of gun violence usually do not make the mainstream news at all."

Even by the stringent federal criteria—which we use below, representing but a fraction of all U.S. victims of gun violence—this has been a bloody year.

January

7 - Tulsa, Oklahoma: Four women ranging in ages from 23 to 55 were found in their apartment shot dead with their hands tied behind their backs. A pair of brothers was arrested for allegedly robbing and killing them.

19 - Albuquerque, New Mexico: 15-year-old Nehemiah Gringo allegedly used an AR-15 to kill his entire family—his gang-member-turned-preacher father, his mother, a 9-year-old brother, and two sisters, ages 5 and 2. He also reportedly had plans to shoot up a Walmart.

March

13 - Herkimer, New York: A 64-year-old "loner" died in a gun-battle with police after he killed four at a barbershop and oil-lube shop. He also killed a 2-year-old police dog, Ape, before succumbing.

April

18 - Akron, Ohio: Two men and two women ranging in ages from 19 to 23 were lined up in their basement and shot in the head point-blank. Two men have been arrested in connection with the murders.

22 - Federal Way, Washington: A man with a carry license killed his girlfriend, then shot three other neighbors in her apartment complex to death before himself being killed by shots from eight police officers.

24 - Manchester, Illinois: A man angered over a custody dispute killed five of his daughter's mother's family members in their home, then led police on a high-speed chase. He later died in officers' custody.

28 - Ottawa, Kansas: A man allegedly murdered his best friend and a roommate before raping the best friend's girlfriend, then shooting her and her 18-month-old daughter to death. The shooter, who awaits trial, says he "ain't never hurt no man that didn't have it coming."

May

11 - Waynesville, Indiana: Four people were shot in their rural home. After a search of the home turned up meth, police concluded the killings were drug-related. The following month, a suspect who was already in jail was arrested for the murders.

13 - Fernley, Nevada: A man killed two couples in their homes over Mother's Day weekend, burning their houses. He also slew a newspaper deliveryman and stole his truck.

June

7 - Santa Monica, California: An emotionally troubled 23-year-old with 1,300 rounds of ammunition killed his father and brother before going on a rampage that killed three more at Santa Monica College. The gunman was killed on campus by police.

July

26 - Hialeah, Florida: A workout enthusiast under scrutiny for sending abusive emails to an ex-employer killed the husband-and-wife managers of his apartment, then murdered four more neighbors before taking hostages. He was killed by police; the hostages were unharmed.

26 - Clarksburg, West Virginia: A gunman killed two in a suspected drug house, then while fleeing shot and killed a 70-year-old man and his 47-year-old son who were in the neighborhood to deliver the local paper.

August

7 - Dallas, Texas: A former teacher and football coach killed his girlfriend, estranged wife, and two of their children before police arrested him.

14 - Oklahoma City: A "weird" 40-year-old man killed his mother, sister, niece, and a 7-month-old nephew with a .380 pistol. He currently awaits trial.

September

11 - Crab Orchard, Tennessee: A man and a woman were arrested for killing four people, ages 16 to 22, in their car during a robbery that followed a botched marijuana deal.

16 - Washington, D.C.: A military contractor who claimed to hear voices murdered 12 ex-coworkers with a sawed-off shotgun at the federal Navy Yard before he was killed by police.

20 - Rice, Texas: A woman killed her husband, their three sons, and herself in their apartment. The husband had been arrested for a domestic violence charge two weeks before.

October

9 - Paris, Texas: Four people were found dead in a home; it's not yet clear what transpired or who killed them.

26 - Phoenix, Arizona: A man who was allegedly thrown into a rage over the neighbors' two barking dogs killed the animals, then his four neighbors, then himself with a pump-action shotgun.

28 - Terrell, Texas: A man who "appeared to be intoxicated" killed five people, including a convenience store clerk, at four locations before police caught him.

29 - Callison, South Carolina: A man killed his ex-girlfriend, her parents, and two of her children before taking his own life.

November

7 - Jacksonville, Florida: Two men and their girlfriends were killed in what appeared to be a planned drive-by shooting. The suspects are at large.

23 - Tulsa, Oklahoma: Four people were killed in a suspected meth house. No suspects have been arrested.

December

1 - Topeka, Kansas: Four people were killed at a house in the town's southwest section. No suspects have been named.

3 - Alma, Arkansas: After arriving home with them, a man killed his daughter's boyfriend in the car, then killed his 4-month-old grandson while he lay in his car seat. He pursued his daughter and four-year-old granddaughter into the backyard, killing the granddaughter before turning the gun on himself.

3 - Erwin, Tennessee: A man with a record of domestic unrest killed his wife, son, and daughter before committing suicide.

8 - Manchester, Connecticut: A man killed his ex-girlfriend and two friends, then fled with the couple's 13-month-old child. When confronted outside by police, he set the child down on the ground and fatally shot himself.

Sources: Reddit; USA Today; Huffington Post