Officials say the Glock handgun discharged while Maj. Donald Lamar was demonstrating to Bristol County deputy sheriffs how to safely holster the weapon.
The bullet ripped a hole in Lamar's pants but missed his leg and foot.
Sheriff Thomas Hodgson says the officer made a "gross error in judgment" by not emptying the weapon before the class last week.
Lamar, a certified firearms instructor since 2005, was transferred to another division and will not carry a firearm while the incident is being investigated.
