Felons and the mentally deranged are banned from possessing guns under any circumstance, I honestly don't know how you plan to improve upon that system while retaining the rights of lawful owners.

It's very optimistic to assume that enough mentally deranged people that "detected" and thus banned. In fact many of these terrible events might be such people in the end. Mentally stable and sane people won't get religiously brainwashed. Same for supremacists.