Had this happen a few years back, now I use Varget powder and no more problems. In my case, I was using IMR 4895 in some pretty warm loads. As the chamber heated up, the powder got hot and really increased the burn rate. I was driving the fragile bullets so fast they came apart. Actually, they destruct in the bore and a faster twist rate will compound the problem. Varget powder is rated as an "extreme" powder and will not increase burn rate near as much as other powders when it gets hot. I also changed to 55gr Nosler ballistic tips. They hold together better.