John

Quite a common problem and not something to be greatly worried about.

1. Often older DR's have not been serviced and the striker has become pointed, the wrong shape or whatever. (FYI, when I buy a new DR, this is one of the things that my gunsmith looks at ebfore I take it out to the range).

A gunsmith can shape the firing pin correctly and / or adjust the length the firing pin protrudes.

2. Fed 215 Primers are the ones I have the most problem with this happening - it seems to be the softness of the Primer metal.

Not sure if you reload but you may need to try some of the other primers.

As you say, you have to "bang" on the bottom of the gun to get the strikers to return far enough back to allow the gun to open.

MAKE SURE AT NO TIME anyone tries to force the barrels open by putting the gun over the knee !!! I have seen it tried and it will bend / break the strikers.

Hope that helps.