What size WSM are you using?? I have a 22 load the ring to capacity and will still have unburned fuel after 14 hours. Another question is what are you cooking at 150 degrees?
I was cooking an 8 lb. butt, started with full ring unlit then distributed 20 lit evenly on top. Pretty day mid 80s a little windy. 22"
Just a thought. How are you supposed to reach 203 internal temperature cooking at 150.........
If it was windy I could see a full load (15-20#) of charcoal being consumed in 10.5 hours.
My last cook was with left over coals and the new version of KBB and I think it was a 15# bag (but it could have been a 18#er) that I started with 1/2 - 3/4 chimney of the left over coals, that ran overnight @ 220 for >12 hours and I have ~1/4 of it left over. There was no wind that night.
I measure my temp on the grate with a Maverick.
Sorry I have no recommendations to extend your run time.
Since you are cooking at ~250 I would think you could get 14 hours + with calm wind conditions on a 20# load of charcoal.
How are some of you getting 15 - 18 and more hrs. out of a ring ? 10.5 at 150 degrees seems to be my limit, with regular Kingsford.
You using a different fuel or what ? Did a butt yesterday and had to add a little fuel toward the end.
Appreciate any help
Next long cook I am going to start with a full ring unlit and 12 lit on top, see how that works. Course the smoker is new maybe a little more smoke and
grease will help.