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I cooked 6 butts at 50 lb. a while back. I was using a CGS Adjustable Rig and everything fit with ample room to spare. If I put them on edge on the bottom rack and flat on the top I believe 10 was doable, maybe 12 if top can be on edge also. The way I was setup there was room for heat circulation between all butts and I am sure that 10 would be similar. I think 100 lb. might be a stretch to cook at once without having circulation room between. The cook took about an hour longer than when I cooked 2 butts in the past. The only issue I encountered was my grease catch pan overflowed. I had to remove everything and empty the pan which was very dangerous. I now have a much larger catch pan if I need to do this again..
They were cooked at 127° for 1 1/2 hours then CI seared. These were ground chuck from Fresh Market BTW. Maybe if I ground my own meat they would be better but it was time to get this cooked and I thought "Why not try it?" If I cooked for a shorter time may have helped but it was packaged ground so I preferred it was cooked longer to be safe. 1 hour was recommended for home ground. They were nicely pink inside.