With no indication of bullet weight over that powder charge, it's hard to estimate where your pressure is at, but loose primer pockets are a definite indication of high pressures. Totally unrelated to the case head separation you had with the 260, that was a headspace issue or a chambering issue- possibly too much protrusion. We're running Retumbo in the 6.5-284, at 59gr under a 140 VLD. Velocity hovers around 3050 on a 24" tube and there's no signs of pressure and great brass life with both Lapua and W-W yellow box brass. We went as high as 56.5 with the H4350 but the velocity just wasn't there, some 300fps slower than the Retumbo loads. You may have a bad batch of brass, or some other issue causing pressure spikes large enough to affect the web. There are a lot of things worth looking at, but I think I'd look at the brass first.