Any kind of case rupture, even something as "minor" as a split neck will result in a flyer. The first deer I ever lost was due to a separated 303 case sending the bullet low at a range of just 30 or so metres. Unfortunately it wasn't low enough to miss the deer all together and I left a wounded deer somewhere on the ground because the dog lost the trail.
Recently I was shooting with my 308 and I was getting a split group. It left me puzzled and frustrated, and at first I thought something had come loose in my scope. I had a nice 3 round group near the bull of my target and then a loose collection of shots about 8" lower. It wasn't until I got home and noticed that some of the cases had split necks that I realised it was the ammo causing the inconsistency.
Personally, I'd weigh the S&B brass in for scrap. Current price is £2.30/kg (well, as of about 3 months ago when I weighed mine in.)