About that bit I'm using... I hadn't meant to be mysterious about it, I just didn't know what it was called. SRP member RoyalCake gave it to me a couple years ago, and the markings are very difficult to read. So all I knew was 'it's my special drill bit'. Not very useful to anyone but me, actually!
Well, here's a link to where you can buy a set of them:
https://www.grainger.com/product/CHI...Code=P2IDP2PCP
They're high speed drill/countersink bits. Pricey, yes, but for drilling out razor pins, they should last forever. The one I'm using is a #2. Google turns up a lot of hits for drill countersink no. 2.