Take a look at HiBC's post on ejector pins in another context. When a part is ejected from the mould, the ejector pins leave a circular mark, usually with a tiny bit of a rim around it. That means the part was made using (metal) injection moulding. If you see those marks on a gun purporting to be made from forged or machined parts, be aware of what they mean.
In one case, a gun that was put up for sale as a Civil War era antique had back and front straps showing ejector pin marks. The prospective buyer was warned and withdrew his five-figure offer for the "antique" gun.