Oldandslow,
Some other random thoughts:
You mentioned deep primer strikes. In addition to checking firing pin protrusion as Jimro suggested, check your headspace. If for some reason it is long, then when the primer fires it will back out until not much primer pocket is still supporting the sides of it.
Have you checked your primer pocket reamer's profile? If it's cutting too much shoulder at the perimeter of the primer pocket, again, you may be left with too little brass to properly contain the primer cup.
When shooting low pressure loads, like wax bullets, it is often necessary to open flash holes up a bit so the primer doesn't back itself out so hard. The normal spec for a flash hole is 0.080" ± 0.010". So you could try opening a few of them up to 0.090", and still be in spec. A number 43 drill or a 2.3 mm drill will do that.
Can you get hold of a
flat bottom small hole gauge and an
OD thimble micrometer to measure the inside diameter of your primer pockets with? If not, waxing one and pushing some JB Weld in to get a cast you can measure will tell you if the hole is out of round or has been too aggressively profiled.