It would be interesting to see a type of gun, shots fired, people hit study of mass shootings to see how much of an effect the type of gun has. I get the theory of a gun with lots of bullets and no need to constantly reload, allows more kills than a single shot, regular reload weapon. But what difference does it really make?
Hungerford - 2 x semi auto rifles and a handgun - 16 deaths, 15 injured
Dunblane - 4 x handguns - 16 deaths, 15 injured
Cumbria - 1 x shotgun, 1 x bolt action rifle - 12 deaths, 11 injured
Plymouth - 1 x shotgun - 5 death, 2 injured.
Another factor is movement. Dunblane was all inside one school, Hungerford and Plymouth were over shorter distances, but Cumbria was over a long distance as that shooter drove around.
Another factor is the shooter. The least known mass shooting in the UK was Monkseaton in 1989, when a male took his father's shotgun and shot at 17 people, killing 1 and injuring 14.
I am not convinced the type of gun is a major factor in how many die in mass shootings.