When I started out in CAS, I had a bag full (around 300) 45 Colt balloon head cases, so I thought I was off to the races. My brother gave them to me, and he and I had reloaded them many times, mostly with Unique powder. We shot them in a 1917 New Service.
So I attended a shoot in a little town south of here, and borrowed a 1892 Winchester repro since I didn't own a match rifle yet. On about the third shot, I had a case head separation which ended my day's shooting...particles in my right eyeball, and a rifle with a brass sleeved chamber.
I was able to fix the rifle without too much effort, and since it was borrowed and I was using black powder loads, I thoroughly cleaned it too. I discarded all of that balloon head brass and purchased 1000 new Starline cases, which I've been loading and shooting ever since.
That's my experience with balloon head cases!