Apparently this isn't a rare problem.
My 629 front sight plunger spring has 'sprung',
it puts zero pressure on the small cylinder that is supposed to hold front sight.
It's so loose, the sight fell out.
S&W wants me to send revolver in for service,
but that's very difficult at the moment.
Have a fiber optic front sight on order, should arrive in a day or two.
Any easy fix for this issue?

Drive out the pin, remove the spring and plunger, replace spring, reassemble.

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