Im not US citizens and i know this topic is hornest nest for you guys, but somehow i want to help by pointing on some things what i see - mayabe because im not personally involved
1) There is problem with violence and mass attacks in US - in some post (not just here) i kinda feel that some ppl dont want recognize it. Now the existence of problem doesnt mean its guns fault and that they need to be restricted
2) It seems that most common targets are hospitals and schools, that indicate more deep moral problem because those places are ussually protect by society moral code
3) Ussually attackers dont care about consequences - i would say that is also huge factor and indicator
4) Fireaarms makes those attack easier - hold your horses, not saying restrictions are way how to solve this, but superiority of firearm over stick is just fact
5) Gun community seems to just oppose every restriction and instead promotes arming everybody - we all want to protect our hobbies (right, if you want) and somehow expand it, but arming everybody isnt solutions. In same way, there shouldnt be just blind opposition against "efforts" (maybe wrong one, but still effort) to solve or decrease number one problem. Instead gun community should say - we dont think this will work, what about this...
6) I can be wrong in all points, im not local, i dont see into local politics or whats your pro-gun groups doing
While keeping point number 6 in mind, i would say the problem is morale and stress related, its not created by guns, but its multiplied by gun (gun itself is force multiplier so...). BUT if is majority of attackers "mentally not well people", you dont need restrict guns for all, just for those ppl. Certanly not by SBR braces and other bonkers ideas.
So i would propose to get rid of all restriction on semi-automatic guns (but you will still have to settle with limited mags in some states i guess), just cathegorize it as its common in Europe (hunting guns - looong, limited mags, long guns - essentially what ppl see as rifles, short guns - SBR and hanguns - just pistols and revolvers) in exchange... and now read it till end before you enter into your rage mode - need of gun licence to buy gun, felony in case if you sell or give gun to somebody without gun licence, obligation to secure gun against miss-use by person without gun licence or theft
Gun licence - given to US history and citizens feel about government, there is few ways how to do it:
1) Federal and/or state licence - if you get federal licence, it applies in all state, state one is just local
2) Acredited organization/company - government give licence to some organizations or companies making tham responsible for managing gun licences without giving data back to goverment
Requirment to get gun licence should be based on extense of gun licence (mentioned cathegories) - health check, test about gun laws, use, maintance and so (in Czech its 28 question + 2 first aid question, from set of about 600 questions), practical test - demonstating that you can handle said gun cathegory.
Gun licence should be mandatory for new shooters, current gun owners would keep current status but would be allowed to sell gun only to person with gun licence or licenced seller + if they want new gun, they have to get gun licence
Another part what you will propably hate - every gun should be traceable. Again, given to US specification, not by goverment without cause. Meaning that every gun and main gun part will have serial number and serial number would be connected to concrete gun licence. These records could be managed for example by manufacturer and accessed by government only in case of investigation of crime (like gun found on person without gun licence, on crime scene etc...)
All this should be supplemented by option to sell previously not registred gun to licenced seller or submit it to LE without penalty
Similiar system already and sucesfully works in Czech republic and some other states.
Its not perfect, but its reasonable effective with good compromise.
The thing is there is no magical solution. As we said before, problem of mass attacks isnt created by guns and instead its deeper moral and social issue, but untill population would not be reasonably sure that some "meth head" cant get legally gun, gun community in US will face more anti gun moves
Its also important to aknowledge that (outside some bussiness and populists lobby) regular ppl just worry about next mass attacks and see guns as meaning how to carry out such attacks
I dont mean to force my hand into your bussiness, just offering my view on things and if i offended somebody i appologize. Its just my opinion and if you want, pick some thoughts from it or just ignore it