The new world of optical sights for pistols.
Oh, how things have changed.
When I bought my first RMR (Ruggedized miniature reflex) sight, I had to purchase the sight. Then I had to ship my sight and slide off to a machine shop. The machine shop milled out the slide to fit the sight and mounted the sight.
Today, many manufactures are selling optical-ready pistols. Add to this, there are numerous types of sights available. The choice of pistol and sight has become very confusing.
This posting by the National Rifle Association does an excellent job of clearing up some of the confusion. I found it very informative.