Here is my $0.02 on this.
6.5 hours too short time, 250 too high temp. Brisket needs to be done low and slow to make it tender.
Here is how I do my briskets.
- Slather brisket with my mustard slather (16oz bottle cheap yellow mustard with 2 TBSP of Worcestershire sauce added)
- Apply rub
- Wrap tightly in saran wrap, place in a pan, and place in fridge for at least 12 hours
- Remove from fridge, unwrap and re-apply rub as needed, leave out while I prep smoker
- Smoker temp is 200 - 225 target temp is 215
- After 4 hours insert probe and Spritz every hour or so for remainder of smoke (8oz Jack Daniels, 6oz apple cider, 4oz water, 2oz cider vinegar)
- Smoke till IT is 190 - 195 (this takes 1.5 hours - 2 hours per pound)
- Pull and place in foil pan with 1/4 - 1/3 cup spritz and cover with foil
- Place pan in towel lined cooler and let rest for several hours. (I have gone 4 hours and it was still very hot)
Hope this helps ya out.