My god, is this a puzzle on how to assemble a rocket launcher? Guahaha

Someone PLEASE check me on this one. I am by no means knowledgeable on weapon assembly, and my Google-fu can only help so much. I'm certain "ammo restraining" isn't right, but I don't know the proper equivalent English term for 弾押さえ.

The gun is tagged on Pixiv. It's an M20A1B1 Super Bazooka.
http://www.liberatedmanuals.com/TM-9-1055-201-35.pdf has everything we want to know.
http://www.inetres.com/gp/military/infantry/antiarmor/M20.html is easier to read but vague. Between Barrel Latch and Barrel Fastening, one is going to be the front barrel assembly and the other the rear barrel assembly. I'm hoping I guessed right on the contactor latch assembly, and I'm pretty confident on the firing mechanism group.
I'd do more, but I'm so far behind on my other translating projects. Maybe in the future.

Appreciate it. Unfortunately, neither has quite what I need to pick out the right terms definitively, which is a numbered, labeled parts guide like we see here. The PDF has several exploded views with parts numbered, but none of those illustrations actually name the parts. There are some disassembly steps shown with parts named, but none of the named parts seem to be those for which I'm unsure. There's a wonderfully complete list of parts, but none of the names are paired to any images, much less the numbered parts on the aforementioned images.