Years ago, I had a battery powered fish hook sharpener that worked a treat for such. It ran much slower than a Dremel tool, and thus was not prone to skipping off in a random direction.
These days I would reach for a sheet metal deburring tool and simply give the sharp edge a scrape to round it off.
Really, it takes so very little of a sharp edge to shave bits off a soft lead bullet. It takes very little material off off that edge to completely change that, too.
