These two articles give a lot of info and perspective:
http://www.nccdglobal.org/sites/default/files/publication_pdf/ons-process-evaluation.pdf
https://www.motherjones.com/politics/2014/06/richmond-california-murder-rate-gun-death/
From reading them, I am not sure if it scalable or it is dependent on unique circumstances and people.
I am going to read some more.
I think the idea of identifying those tiny fraction who do almost all the gun crime and locking them up for a while and also offering them some way out of that lifestyle makes a lot of sense, otherwise they will just keep shooting people, I think it's a lot cheaper too in the long run. Dead bodies and murder cases cost money. We will have to see how it works in Sacramento, that's a city of 500,000.