Pretty much agree with Otto. Nickel plating can weaken brass, so I avoid it for warmer than target-to-medium loads, other than for the first firing, which can be full pressure as a rule. Its main advantage is corrosion resistance in a leather belt loop. Save loading nickel for safari or duty carry and other applications where you need weather resistance but are unlikely to recover the brass.
Winchester primer cups are not the hardest, IME. Usually OK, but since you are having trouble switch to the CCI magnum primer or to a Russian made Wolf or TulAmmo magnum primer to get a harder cup.
Increasing complaints about Remington and Winchester brass of recent manufacture being too soft are surfacing in various calibers. Outsourcing is being blamed. Bite the bullet an buy some new
Starline brass. It has about half the weight variance of the big brands and is not too soft in the head. Currently on back order until October 17th, but I think you'll find it worth the wait.