It is perfectly obvious, but perhaps worth noting for folks that are new to fitting a stock iron...you do not remove any metal from the gun!...only from the iron. Usually the depth of the "channel" in the iron is too shallow and binds up when attempting to attach it to the gun. You need to remove material from the bottom of the channel. Some folks attempt to do this with a Dremel tool, but that is a bit hard to control. The best tool for the job is called a "riffler" file and can be obtained from places like Brownells, but also are usually available at good hobby stores and specialty hardware stores.
It doesn't take too long to remove enough metal to get a good fit. Take it a little at a time. A final polish with some 600 grit emory paper wrapped around the riffler makes the assembly smoother and a little cold blue makes it pretty
(pretty only lasts a little while since installing the stock quickly wears through the blue).