Las Vegas Strip massacre (Las Vegas, NV, 2017) 58 dead, 546 injured, weapon: guns
Orlando nightclub massacre (Orlando, Florida, 2016) 46, 53, guns
Virginia Tech massacre (Blacksburg, Virginia, 2007) 32, 23, guns
Sandy Hook Elementary massacre (Newtown, Connecticut, 2012) 27, 2, guns
Texas First Baptist Church massacre (Sutherland Springs, TX, 2017) 26, 20, guns
Luby's massacre (Killeen, Texas, 1991), 24, 20, guns
San Ysidro McDonald's massacre (San Ysidro, California, 1984), 22, 19, guns
A couple of non US ones:
Hungerford, Massacre, (Hungerford, England) 17, 15, guns
Dunblane Massacre (Dunblane, Scotland) 18, 15, guns
Do you want to carry on with this line of argument? Because I suspect, you are going to run out of examples before I do.