OK guys, I had a chance to load up some 10mm and give it a go at the range.
10mm 180-gr. Sierra FMJ bullet
Used Starline brass
CCI large pistol primer
I loaded up fifteen of these guys and shot them through my stock Glock 20. Slow, aimed fire just like with the DT that got me the terrible results the first time around. Result:
And just for fun I gave it another go with a box of .40 S&W with my KKM 10mm->.40S&W conversion barrel.
I did not bring any DT to the range this time - should have but forgot to toss it in my range kit the day before.
Next time I will bring DT, and my next batch of 10mm will have a little more powder in there. In fact, now that I know my dies are set up right, I may load up 50 rounds, starting with the level of powder I currently have and ending up at max load. See if there's any effect on accuracy as powder levels increase.
So far it's not looking good for DT, for me at least.