I have had terrible results trying to hatch BCMs until my last attempt. My basement is way too dry to do a dry hatch... Relative humidity 8-12%... Normal settings caused a lot of late quitters... I got a digital hydrostat with humidity pump and set it at 40% for days 1-20 and then 65% for day 21. This was close to what the seller recommended for her eggs(brenda little). 11 eggs developed , 8 hatched on their own and I helped 1. Pretty great results for shipped eggs. I will definitely use this method next time as well.I like your idea about using a hot water spray bottle!
With BCMs since last year I have always done dry hatches until day 18. I don't know if it's because the BCMs have an extra paint jobbut they don't seem to lose moisture in the shell the first 18 days as easily as other breeds. When I did leave water in there, I had a bunch of too large chicks unable to turn around in the shell and a horrible live hatch rate. Now I dry hatch and it's 90-100% success.