I believer the main charge in a primer is a propellant, not a true explosive.

I believe the stray primer contributes to chamber pressure, but not the difference between normal pressure and a barrel bursting pressure.

There are a couple of "I believes" up there, so I'd really like to see some data. And, I'll have a look at load data to see if there are reversals with "hot" and "cool" primers as to chamber pressure.