I've made a few of these for myself, both in leather and in Cordura.
The inside system of separators is hard to put together well, with either a complicated stitching process or a lot of material involved, depending upon the actual interior configuration.
The nice thing about a "six-pack" of M1911 magazines is that, with the seventh mag in the gun and one round "up the spout," you're carrying exactly one boxful of cartridges, 50 rounds.
Further information is available on request, including a drawing. I guess I could take a photo of one, but I am technologically challenged and don't know how to add it to a post on this forum.