Or a brass rod, any plunger that fits closely so that hydraulic pressure will build to expel the spent primer when the plunger is tapped. Sometimes you can bulge the case if you hit too hard, or if the primer is crimped.
Messy, and the cases must be dried.
I find it faster to just tap a pick into the firing pin dent at an angle and lever them out. Faster and tidier.
Also have a RCBS decapping tool which does the same thing.
Berdan caps are not necessarily the same diameter as similar Boxers; some are quite different. Altered a priming stem to suit. The Lee Loader technique can be used as well. Place the primer on a hard smooth surface and tap the case onto it.
Be careful not to crush the Berdan primer when seating.
