A Miami-based political committee has proposed a constitutional amendment that would ban possession of “assault” weapons in Florida if approved by voters.The proposal, backed by the committee Ban Assault Weapons Now, was posted on the state Division of Elections website this month. The committee had raised nearly $410,000 since March, while spending almost $284,000, according to finance information. The expenditures included $75,000 last month to a California-based company for what was described in the finance information as “petitions.”