40 years ago when I started reloading, "harder" military specification primers were not readily available. In fact, about the only primers I could get my hands on were CCI. In 223, I used small rifle regular, magnum and bench rest primers interchangably and fired the rounds in rifles with and without floating firing pins with zero primer-related issues.

I can't (and won't) say not to use the military specification primers - they exist for a reason - only that in four decades, I have not encountered the conditions the military specification primers were made to address.