So you are storing them in your barn, but the temps would vary. Could it be the variance in temp that is bothering the viability? I am just as curious as you.. Because our temp varies here greatly. Day times right now are just like yours, as are our nights.. However, last few hatches the eggs were collected in extreme temperatures. High 90's during the day and 50's at night. Of course it is not AS extreme in the barn is it is outside, but I'd be willing to bet the barn stays somewhere in the early 80's in the hottest, and drops down in the 60's during the night. I leave all windows open 24/7. I know the barn would stay cooler if I didn't, but it is fresh air and I believe it's very important.
I'd say my Barred Rock eggs are less bothered by it.. but still my hatch rate is lower than I am used to in the spring/fall.
I could very well store my eggs in a better place, but I often forget about it. I am so busy with work/chores/life that it just gets put to the back burner. Usually something distracts me and I forget the eggs in the flats in the barn. Whoops...
I need to get a routine going and I won't be so careless. I am not selling hatching eggs, otherwise I'd be much better at keeping them in the right environment.
I'm curious if I put them on a breeding formula of feed if that would help.