Hi,
My only reaction is the effects of high temperature on your brisket. There are reasons why corned beef (brisket) is simmered rather than boiled. If assaulted with high temperatures, the meat (muscle) contracts. By weight it may be the same critter, but volume it will be a shrinky dink.
Now as for the bbq element, I will defer to those who know.
Regards,
CAthy2