By all means this is all you ever need to know on the matter. It worked for me. Don't panic, it's a DIY fix that is both easy and permanent: I haven't had a misfire or slam fire since I did this:
I am having the exact same problem of yours..I had to install a G&G Steel Cocking piece when my original broke (brute force is bad force, sometimes ).
And now the rifle slam fires when cocking the bolt..if I push it down a little, while pushing it forward to cock it..I might get away with it and still have a chance to fire correctly, but it slam fires 75% of the time..
I am going to try your method and see if it works Thanks for the explanations and pictures..they are going to help me, for sure!
...time passes by and..UPDATE:
I just finished tinkering and completed what Ripperkon did. I just tried it out and man: you saved my back.
It might be a little early to be sure, but I suggest this is made into a sticky or something like that..you Ripperkon deserve some real +1 in my book!
The picture I am referring to (thanks Ripperkon):A step-by-step analysis to the problem and workaround:
1a. It seems that the G&G Steel Cocking Piece is slightly off spec (ta-daah old news, right? ) and it needs a bolt stop that pushes upwards a little more, against it.
1b. To have it raise, the trigger (on which the bolt stop sits on) must be raised as well, but there is no way to adjust the sear position..hence the shimming.
1c. I used your exact same little round shim, shaving it on the sides so that it does not scratches against the trigger metal plates (some sand paper is enough).
2. That small increment in the sear height transfers over the bolt stop, which goes on par with the cocking piece.
3. You'll see the cocking piece "cocks" correctly, because when you cock the bolt you'll see it protruding way out of the bolt itself (it will stay with its "ass" back out from the bolt, towards you, for a good half).
I know it's early to say, but I've been dry firing like crazy with and without the magazine in it (with the mag in this slam firing problem usually got accentuated) and the problem is gone!
Some sticky this and +1 Ripperkon. Once again, this forum rocks. Don't tell anyone though, this way the knuckleheads will keep out