I invert my drill in my vise (like a mini lathe), and tighten my adapters in the chuck (threads & stem section only) and turn them down to exactly the size taper per my chosen BH. It works really well! I remove steel by bringing a mill bastard to bare, lightly pushing over the adaptor to reduce the dia. It doesn't take much, so start slowly and keep checking for the desired fit ***please use eye protection*** Every BH requires a slightly different taper. Yes all are ~ 5 degrees, but the truth is in the detail. Note: most adapters require the most reduction at the rear of the taper, so leave the front un-touched initially.
I can get any BH to spin perfectly and will always fit the adapter flush to the back of the BH. It makes for a very clean and strong fit.
Kris