I used to go to the Signature Room in the Hancock building once in a while, on the 95th floor, for lunch. They had a wonderful buffet at lunch and on St. Patricks Day they would feature corned beef. The chef there must have thought he was dealing with roast beef because their corned beef was tough and rubbery, obviously not cooked long enough.
I've cooked corn beef brisket in the past, so I know this answer. My husband does not care for it, so I haven't cooked it for many years, and it's likely outside diet parameters now.
Corned beef is something I prefer to buy from the deli, pre-sliced. I've made it a few times, but it is a lot of work and, frankly, not as good as the stuff from the deli.