When I was decapping a lot of .357 cases, I noticed a few (2 out of 100) primers were bulging in a convex shape, even the firing pin dent seems to have been pressed out evenly, so I doubt the decapping did it. The other cases (98 out of 100) looked normal, big dent for the firing pin & the primer face slightly concave.

Is this an overpressure indicator ? There were no other obvious signs. The load was 5.5gr of Red Dot with a 158grFP bullet, I know this is pretty much the "never exceed" load. I have used this load before & never noticed any problems, the recoil didn't feel excessive in my Taurus LBR when compared to shooting factory magnum loads.

Should I just ignore it, or step the load down a touch ?

Thanks in advance.