If it's current day, he's is futzing for the camera.
The only time I know of when you mess with the metplat of modern bullets with good reason is in high precission shooting, trying to make the metplat a consistent size/shape. Certainly not done with a file.
One exception is when using target bullets for shooting animals. Some will widen the metplat making the hollow point larger to peel the jacket off when it hits the game, doing more damage. IMO that's not good reason, it's poor bullet selection. If you're shooting game and you have time to prepare, select a bullet for that job. If you're trained up on the target bullet and can only use those, put the bullet in the head/spine and negate the need for the bullet to not do it's job.
Target rounds (Hollow Point Boat Tails) have very thin jackets, btw. Enlargening the metplat increases the diameter of the hollow point, but the results are largely unpredictable, and it effects accuracy.