This baffled me...so I started to sketch the gun from the images that I'd found...and I realized how gosh darn strange the gun was.
Here's a good example of what really took me by surprise.
The pommel is the part right beneath his elbow, and goes up into where the trigger should be placed near his hand. Closer inspection of all versions I could find of the gun...shows there's no trigger. At all. Nothing akin to a trigger, even. That little piece that he's holding? Logistically...that should be a place to store bullets, or it could be a handle...for the trigger...except there is no trigger. Instead, he looks more like he's pressing the safety...which I find really funny.
Look right in front of the block he was "holding". See that little square? that should be a safety or something...but it looked like he was using it as a trigger.
I know, it seems a bit like "well what does it matter?" and it really doesn't. I love details, and I was trying to find the best match when I saw this. The gun, which looks fairly accurate and plausible from the first glance...makes absolutely no sense when you really get down to it.
Its funny how things work like this.
Anyways. My original plan will still work...but I think I might just get a machine gun as a fall back, that way if I don't manage to finish the weird-totally-doesn't-make-sense gun, I'll still have something for AnimeFest. ;3
But no matter what, I'm not displeased with my "discovery". It will make the gun all the more fun to figure out!