So yesterday I had something happen I've never experienced before. First time loading 10mm, although I've loaded a lot of .40 S&W.
As always, I very gently expanded the case mouth just enough to get the boolit started. After I seated the boolit, I checked the case mouth diameter to see how much of a taper crimp I would need. The case mouth was 0.423", which is nominal. So apparently it doesn't need a crimp, and I confirmed that they chamber in my gun. I've never had this happen though where I didn't need ANY crimp, and I'm hoping there aren't any issues with the boolits moving in the cases. Running 7.5 grains of Power Pistol under a 170 gr. MP WFN solid, PCd.