Striker Boing ?

[Peter Laidler]

Before you go to all that trouble and the expense of buying new spring and possibly a stripping tool, just test the weight of the mainspring.
Action fired, spring weights to be between 7 lbs low and 9 lbs high
Action cocked, spring weights to be between 14 lbs low and 16lbs high.

That's what we'd do................

You could rinse it out in petrol and blow it through with an air line but, in my very limited experience with these things, if it only happened with one round, I'd say it was an ammo fault