I like this but have no fyayking idea what gun that is.  
Sorry didn’t read on through.

@ZhaoZoharEX
 
Months-late-reply on this, but as the original commissioner, I can answer some of these questions for you.
 
The gun itself is a sort of mish-mash of parts - the majority of the body is based off of the Australian McCrudden Light Machine Rifle prototype, with an added bayonet lug and front sight. The McCrudden LMR has a pistol trigger grip and loads from a horizontal magazine on the right-hand side, but I revised it in sketches to feed from the left and eject to the right, as well as to take a very short magazine, hence the easiness with which it’s being held close to Lightning’s chest. It’s also scaled-down compared with the real-life weapon to, as you say yourself, more a carbine length. My intention when doing so was to place the weapon as a semi-plausible cross between a machine carbine / battle carbine, and a short semi-automatic rifle. A few extra details staying only in sketches and the angle of the piece mean it’s a bit harder to see some of these bits and bobs.
 
The insignia is also somewhat headcanon-ish, representing a rank around that of a Commonwealth-military Corporal. One stripe / chevron for the equivalent of a Private First Class, second for Lance Corporal, and the circle indicating a junior NCO. In all honesty I hadn’t refined the fictional system very much at all when I commissioned this piece, so I picked out something I found appropriate.
 
The trigger discipline I didn’t specify in the original commission discussions, and was content with the artist’s decision to put a finger on the trigger as a representation of imminent battle, but I certainly understand the lack of context for such a positioning.
 
I’m glad you like the piece overall though, I was super-happy with it and definitely still am - and I don’t think your noticing of details is at all a negative thing, just a testament to having a lot of knowledge on the subject ultimately.

Okay, I’m really sorry, I like this drawing of Dusty, really I do. I always like the soldier Dust and even have a whole headcanon related, but there are a few things about this pic that kinda bug me and I can’t tell if it’s legit issues or if it’s just the autism kicking in. Please bare with me.
 
What is up with that gun? I can’t tell what kind of rifle it’s supposed to be, is it a musket? Because if so, she’s holding it as if there was a pistol grip. Is it an assault rifle? If so, I can’t see a magazine which most if not all assault rifles have. Shotgun perhaps? No, I don’t know. It looks like a carbine of some sort, it’s a little short to be a full size rifle, but I don’t think it’s short enough to be considered a carbine either. I dunno, the gun just bothers me too much, I’m sorry.
 
Also, she’s a soldier yet not using trigger discipline? I’d say she might be a rookie, but the stripes on her uniform imply at least corporal. And while that’s not, say, experienced, that’s not newbie either. Maybe I’m looking too far into this, I don’t demand or expect anything military or related to be 100% accurate in art, fiction, or otherwise general depiction 100% of the time; even I take some liberties here and there with my stuff.
 
Other than that, I like this piece, especially the camo pattern. Coat in general is also really cool too, and Dusty herself is cool as always. I’m sorry if I’m making this seem so negative, I’m really not trying to be, I’m just letting what are ultimately minor details distract me too much.

Badass Dusty.

Lip looks a little odd but otherwise awesome.

Epic