Take it to a gun smith. Now I am in law enforcement and was always a mossberg fan. We switch to 870's and this is one of the reasons why we switched. What happens is that over time with alot of shots (don't know the exact part name) things wear and break. Due to the recoil the safety slams back. This happened to one of our patrol shotguns and we sent it to a gunsmith. Note: this is rare and most will never experience this in their lifetime but it can happen.
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