When I first began reloading, it was the priming process that gave me the most grief. Every manual I consulted said that primers need be inserted such that they were about 4 thousands of an inch
below flush with the base of the case. Many were the suggestions about primer insertion tools but nowhere could I find anything about what to do if the primers would not seat even flush, much
less below that level. It seemed logical to me that high primers were a very bad thing even before I had been introduced to information about “slam-fires”. I had so many high primers that my early reloads were fired single shot in both revolvers and automatics. My first attempt to solve the problem was to really look at a de-primed case and figure that the sludge left in the primer hole was enough to prevent a new primer from seating correctly. I invested in about every primer pocket cleaner on the market, but to no avail. I even started tumbling de-primed brass just to clean the primer pockets. I also tried every brand of primer I could find.
I tried re-seating primers with much greater force, which would bring them flush but deformed looking.  That is with a ram-prime style tool. I broke several Lee Hand Primers trying this technique. I finally stumbled across an article, Guns and Ammo I believe, that talked about how brass cases in the primer area should deform slightly when fired, and would thus need some “repair” before reloading. Now that worked. Here it is.

Problem: High primers or primers that cannot be seated below flush with the base of the case. Cause suspected to be a deformed or slightly shortened primer pocket.

Solution: Primer pocket uniformer tool, not to be confused with pocket cleaners or military crimp removing tools. The uniformer will hand machine (or by drill with appropriate attachment) a primer pocket back to the specified depth for the specific primer size used. I tried the most inexpensive first. Yep, cured the problem right off. But the tool broke with not much use. Same with the next. I ended up with a custom set for large rifle, large pistol (different depth than rifle), and small pistol (same depth as small rifle) with a hand tool from Sinclair. Great, much use, and still going. All my primers compare directly with factory ammo. Throw the pocket cleaners away. These re-machine the pocket brass and that includes the sludge as well.

http://www.sinclairintl.com/product/10922/Primer-Pocket-Tools

See how the pocket shines when the base is set back to specs ? The orange cap is the protective cover to protect the carbide cutting blades.