Yes, I know. I've read about how to do the test matings. That's a source of major frustration for me, I can't seem to get started with a flock of birds that don't have side sprigs. The Davis birds I started with had them (one of the roosters that I hatched out was sprigged, obviously other birds in the flock were carriers).
Now I've got this other flock, from a breeder that shows well, and that seems to have a good reputation. I asked this breeder if they had a problem with their birds throwing sprigs, and they said no. AAAAANNND... I get a flock with a huge percentage of sprigs.
Last year I hatched out some birds from a different breeder that were so abysmal that sprigs were the least of their problems. They weren't even black coppers, it seems she breed color varieties randomly. We ate those, gave the hens away. That breeder had an excellent reputation in another breed, was just getting started w/Marans but she told me her source for her birds, she had shown well, and when I google-stalked her there was nothing but positive mentions on BYC.
My multi-year attempt at getting started in Marans has been very, very bumpy. Like almost all bumps. And side sprigs!