Too many.
You can look up which nutjobs used an AR15:
"There have been more mass shootings than days this year
September 1, 2019 / 4:13 PM
By Jason Silverstein
The number of mass shootings across the U.S. thus far in 2019 has outpaced the number of days this year, according to a gun violence research group. This puts 2019 on pace to be the first year since 2016 with an average of more than one mass shooting a day.
As of September 1, which was the 244th day of the year, there have been 283 mass shootings in the U.S., according to data from the nonprofit Gun Violence Archive (GVA), which tracks every mass shooting in the country. The GVA defines a mass shooting as any incident in which at least four people were shot, excluding the shooter.
The toll of 283 mass shootings includes several high-profile, mass casualty attacks, two of which happened within 24 hours of each other:
A drive-by shooting spree in Odessa and Midland, Texas, on August 31, with seven people killed and 24 wounded
A shooting in a historic district of Dayton, Ohio, on August 4, with nine people killed and 27 injured.
A shooting at Walmart in El Paso, Texas, on August 3, with 22 people killed and at least 24 wounded. It was the deadliest shooting of the year.
A shooting in a municipal building in Virginia Beach, on May 31, where a former city employee killed 12 people and wounded four."
Mass shootings in U.S. 2019: There have been more mass shootings than days this year, according to Gun Violence Archive - CBS News
Latest full data available is 2017, so let’s start there
January 6, Ft Lauderdale airport: 5 deaths, 9mm pistol
March 22, Schofield Wisconsin: 5 dead, handgun, UI long gun
April 19, San Bernardino: 3 deaths, .357 magnum revolver
April, Fresno: 4 dead, .357 magnum revolver
May 12, Kirkersville, Ohio: 4 dead, shotgun
May 27, Lincoln County MS 8 dead UI handgun
June 5, Orlando: 6 dead, handgun
June 6, Sandy Utah: 3 dead, UI GUN
June 8, Eaton township, PA: 4 dead, shotguns
June 14, Alexandria, VA: 6 wounded, SKS rifle, 9 mm pistol
June 14, San Francisco, 4 dead, semi-auto MAC-10.
June 30, NYC, 2 dead, AR-15 style .223
July 1 Little Rock, 28 injured, AK pistol
August 28, Clovis, NM 2dead, handgun
September 10, Plano, 9 dead, AR-15, shotgun, .380 pistol
September 24, Antioch TN 1 dead 8 wounded, 9mm pistol, .40 pistol
October 1 Las Vegas, 59 dead, AR-15 type, AR-10 type, .308 bolt action rifle, .38 revolver
November 5 Sutherland Springs, TX 27 dead, Ruger AR-556
November Tehama CA 6 dead .40 pistol, .45 pistol, AR-15 style
December 7 Aztec NM 3 dead, 9mm pistol
December 31, Highlands Ranch CO 2 dead, AR-15 style
So, out of 157 dead in mass shootings in 2017, AR-15 style was used (though not usually solely) in the deaths of 105. And that’s counting the AR-556 as an AR-15 style, which it’s not. (Gas piston, not direct impingement)
Total murders in US in 2017: 15,129
By firearm: 10,982
By rifle: 403
So how is that not a tiny percentage? 105 killed in mass shooting where an AR-15 style was used is more significant to you than 1,549 stabbings, 7,032 handgun murders.
You have some odd priorities.
Sources
List of mass shootings in the United States - Wikipedia
FBI — Expanded Homicide Data Table 8