The semiautomatic handgun found in a car belonging to Cincinnati Bengals fullback Orson Charles was LOADED at the time of the road rage incident last month ... this according to the police report obtained by TMZ Sports.
We broke the story ... Charles was arrested in Kentucky back in March after cops say he got into it with another driver on an Interstate and waved around a gun during the heated exchange.
Now, we've learned ... there was a middle finger involved.
According to the police report, the other driver admitted he FLIPPED OFF Charles on the road ... and that's when he says Charles pulled out his gun.
Charles says he never brandished the weapon -- though his passenger told cops Orson was reaching for his piece, so she took it away and put it in her purse in the back seat so he couldn't access it.
When cops searched the car, the report says they found the gun -- loaded -- plus, there was an extra clip in the car ... so says the report.
Charles -- who was featured on the HBO show "Hard Knocks" -- has since plead not guilty to wanton endangerment. We reached out to him for comment. No word back.