brother and sister breeding ?

I had a accidental breeding of full litter mates & the results were pretty good. The only thing that I was surprised at, the pups were not as gritty as I thought they would be. The father was basicly a running catchdog & the mother was a great bay dog but not catchy. All the pups I kept track of had all the speed, drive, nose you could want but none of them were what I call gritty.
I wish I knew how to pick the best pups out of the litter. I can only pick pups who have the physical characteristics that appeal to me.The biggest pup in the litter does not always mean it will be the best hunter or have the most ability. I think I will start another topic on this subject.