Divert 50 billion of defense funding annually to the states -- 1 billion per state. Design a gun buyback program that funnels the money from Fed to state to local jurisdictions where the buyback events will be conducted at police or sheriff departments, for example.
Standardize the infrastructure, data collection, and reporting process so that every jurisdiction has clear direction and expectation for deploying and managing the process and reporting results. Pay $1000 to $2000 per firearm - or more than the purchase or street value of most firearms -- to incentivize the turn-in of guns. Make the process anonymous, with no questions asked to the owners. Create a stolen firearm database and track the serial numbers of firearms surrendered thru buyback against the stolen S/N database.
Build or retrofit existing facilities regionally that will be collection and destruction centers. Staff the facilities with good paying jobs. Prevent the destructed materials from being sent anywhere OUS; recycle and reuse IUS only. Quarterly facility audits will be required by the ATF or similar red tape agency to help ensure destruction and funding remains above board. Then figure out how to prevent firearm industry and entrepreneurs from taking advantage of the program and funding. Tax firearm purchases at a greatly increased rate to help create sustained program funding long-term.
Report on measures of effectiveness annually, and make next long-term funding decision at year 8 of the program. Assuming 50% of the funding is truly devoted to actual firearm buyback, that comes to 25MM firearms purchased at $1000/unit on the high side to 12.5MM firearms purchased at $2000/unit annually. Initial 2-3 years would be needed to setup the program, infrastructure, staffing, and facilities. Years 4-8 would commence buyback, with potential 62.5MM guns or more pulled from circulation over 5 year period.