I have some experience with weapons
1911
Glock
Remington 870 (I believe)
AR-15
50 bullets is a lot of ammunition to spray down in such a short amount of time.
I really only see two reasonable solutions to our issue with mass shootings, and our general gun problem.
1) Restrict magazine size on all semi-automatic weapons. Magazine capacity can be debated about, but 5 bullets for a semi-automatic weapon like a long rifle is well within reason considering it's limited use for home defense, and it's use in hunting.
2) Ban all semi-auto weapons, allow bolt action rifles and pump action shotguns un-restricted in terms of purchase ability with current background checks still in place.
The first will allow for current weapons to still be legal, while forcibly limiting the amount of ammunition that can be pumped out in a mass shooting situation. Crack down on black market parts, attempt to force manufacturer to make it difficult to modify the weapon to accept a higher capacity mag. Red flags will be raised when someone attempts purchase parts that allow for the modification of weapons.
The second will simply be a sweeping ban on weapons that aren't deemed reasonable for a civilian to own, while allowing weapons that are reasonable for home defense and hunting.