The 3 top strap holes for optical sights

[Mito]

Are the 3 top strap holes for optical sights in an S&W factory drilled revolver drilled all the way trough?

I was wondering if there was a way to see if the revolver was factory drilled without removing the rear sight and also if it is possible to see the difference between factory drilling and aftermarket?

Thanks in advance.

 

[Plinkasaurusrex]

They are drilled all the way through.
Open .the cylinder and look at the top strap from the bottom