Here is a picture of one of my earlier hot-n-fast briskets cooked on my Egg. Bark was one of my issues too. This one was cooked at 350-375. HERE
is a link to a thread in 2006 when I first started the higher temp cooks.
Now, after a lot of high temp cooks under my belt, in my Egg it seems like 325 degrees or so works better for controlling the cook and for the bark. Maybe the higher temps drive too much moisture to the surface?? I just can't say. You'll see a reference to Ed's advice about uncovering the brisket and ramping up the pit temp at the end which does work. Also take a look at this fast track brisket
article on Old Daves site. I've gotten a lot of advice from him over the years and there is some good info here.
As far as a smoke ring goes, the key would be having the meat temp less than 140* for the longest time possible. A 300+ degree pit temp gets the meat above 140* pretty fast, so the ring will suffer. Now what I do is put a cold brisket on a 200* pit for a couple of hours, hit it with a little more smoke than usual, then ramp up the temp to 325*.
KCBS - CBJ
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Barbecue is not rocket surgery