I have this issue as well.

It starts with either JEI is opening a chest with the gun inside. The model zooms in to the screen for half a second and then the gun icon goes white. You can hold it and fire it, but when you right click to aim, the screen goes black.

Using optifine and another 290ish mods, kind of hard to list them all.

I think it involves OptiFine itself, because running the game without OptiFine seems to make the mod load correctly, at least for me. However when OptiFine is used, the game turns the models to white blocks and the screen goes black. Without it, you can zoom in and all that, and the guns render properly. Looks like until either the MW or OptiFine coders look at it and fix it, we'll have to stick with the game being slower in general to load the mod.