For 1.0 (launch) magazines are going to be quite simplistic. There are 3 skeletal meshes (the mag mesh and 2 bullet meshes). If you have more than two bullets in the mag both bullet skeletal meshes will show, if only 1 bullet one of the bullet it meshes will be hidden, if no bullets both will be hidden. Setup for magazines is super simple as well, providing you have the meshes, all you would do is duplicate one of the existing mags, indicate what type of bullet it uses, set up all the meshes/sockets, and tweak a few variables.
While this system works it is less than ideal for me, but in interest of getting weapon master out sometime this decade I will look to improve upon magazines in the first couple of updates. For one I want to go away from the UMG wiget for bullet counts. They hog performance and are a crutch (see through mags or mags with peep holes are more realistic). In the future I want magazines to actually have all of the bullets in them physically and simulate the proper spring movements per shot. I will leave the UMG counter in as an option for those with sci-fi games or feel they need it. Since Update 1 has sort of ballooned out a bunch the magazine updates probably wont make it in until update 2.
BTW, attaching the mag to a weapon is actually handled by the guns. There is a specific socket on the gun that will tell the mag where it needs to lock too. Right now there is no collision between the mag and the guns while you hold them in your hand, but I hope to have that changed in the future.
My first tutorial is going to be making a magazine firearm from one of the marketplace available guns (likely one of ironbelly’s) and that will include magazine setup. In the future we are going to sell “Weapon Master Ready” firearm packs that are modeled by our actual artist (who is **** good). The guns currently in Weapon Master were modeled by me and, well, yeah, I am no artist, but they work for examples :P.