Agreed.
Something that works Very Well if one has a Dremel with a Grinding Wheel and a Drill is to chuck on the Head of the 510 Pin so that the 510 Pin threads are exposed. Then to spin the Drill at a Medium Low RPM while turning the Dremel at Medium RMP. Applying very little pressure with the Dremel. Just letting the Grinding Wheel to do the work.
Once the 510 Pin Threads are ground down to the Desired length, you can Flip the pin around and Chuck on the Threads with just the Head of the 510 Pin being exposed. Once Again, you don't need a lot of Pressure with the Dremel. Just let the Grinding Wheel RMP do the Work.
This Tech make it Easy to get a Flat 510 Pin Head with a Very Nice Finish. Just be sure to do the Thread Length 1st. If you do the Head of the 510 1st, you will have Very Little to chuck onto when you turn it around to do the threads.
NOTE: Safety Glasses are MANDITORY when doing this type of Work.