Thanks for feedback, I wondered how yours came out. Mine was tender after
3 hours and 20 minutes, so I turned off the oven, removed some broth to cook potatoes and cabbage in and left it there for another hour. The broth was briskly simmering after a couple of hours and I reduced the oven temp to 285, then 275 towards the end. I used a large (9 quart?) oval Le Cruset enaameled Dutch oven. It really came out well. We loved the taste and the meat was extremely tender. However, I started with a brisket that was choice grade. I've noticed that some brands of corned beef don't have a USDA grade on them, so they are probably not choice. I've wondered if that's why some of the commercial corned beef I've cooked doesn't get as tender.