[quoteNow the part about graphite I have to disagree,in fact if I'm not mistaken some powders have graphite on the outside coating.Correct me if I'm wrong on that.Anyhow I've used graphite for years on insides of case necks and never had a problem.What say you]
You are 100% correct, graphite is used as a flame retardant to control burn speed. Take your good loads and change the powder burn speed and you have at least a bad load, possibly you'll overpressure one if the conditions go just right.
The primer is enough to unseat the bullet from the case and put it and the powder into the bore before the powder actually ignites and/or begins to burn well. With a max load it can sure cause problems.
There really is a reason powdered mica is popular.
You've done it for years with no problem? I fully believe it. You can possibly continue on for many more years to come with no problems, Like so many other things though it only takes one time to cancel out all the years of luck. It kinda falls in the realm of squibs and double charges.