One of if not most used specialty tools.
Advice:
Use a shaft on the muzzle side (I use a carbon hollow shaft from my RC) to allow pushing the bullet back and forth till you get that right touch on the land. I usually get 1 thous variance with 3 measure per bullet. Measure 3 bullets 3 times, usually get 2 thous variance. If not measure several more.
Buy a tap from eBay, got mine for 6 bucks USD. Make your own modified case from fire formed case, better than HDY one thanks to fire form. Brass is soft, really easy to drill/tap.
Remeasure after 1000rnds. For my TRG 22, 308 Win, after 8lbs Varget, avg 43.5-44gns ->1280 shots the throat eroded ~20 thous (could be from diff batch of SMK, doesn't hurt to remeasure, takes couple of minutes)
Mine is plastic shaft, doesn't matter, bullet touches the land, don't need metal shaft as not jamming bullet. Prefer metal but not needed, HDY knows where to cut corners.