let them get really dry before you pick them, when they r stressed, they produce more capsaicin of course they get to their hottest during really hot dry years, good luck fellow carolinian
paul

The Numex Big Jims i grew in the past were sweet with no heat at all also.

Outside of the usual weather/watering factors it's just known to have a lot of variance.

Did you let them turn red? Even still mine have not had a ton of heat. I read that it is a plant with a high degree of variance.

I wish I knew how to help. I haven't grown Big Jim's, but my jalapenos are quite hot this year. Weird thing is that in years past they haven't always been this hot (same brand/variety).