Originally Posted by havasu
So, the gun was worked over then?
I don't know about worked over, but loose tolerances on slide to frame match ( a known Glock bonus ) coupled with a weak spring would probably do the trick.
The metal slide would be in motion with the rest of the weapon headed back and it would only take twice ( I think ) that force on the forward change of direction plus the compressed weight of the spring to achieve the desired result.
If you take the spring out of the weapon, leave the magazine out and simulate, you will see what I mean.