It only occurs once in 50 times or so????

Sounds like operator error to me, possibly aggravated by a mechanical problem. Or weather.

Assuming the bolt/trigger is clean and free moving (I only use Eezox in these applications!)

I'd check bolt/stock clearance, then put in an over-strength striker spring, assuming trigger adjustment specs are in-bounds.

Something is not right, and I don' think it's the gun's fault....Unless one has the very rare lemon...

The only true cost of having a dog is its death.