They are deffinitely not M31-A1's. They would fire a 4.5mm caseless round and would be in a standard longarm configuration. However, they could well be an evolved version created by a rival manufacturer. I don't buy them being Ronins or WAA's either. Both are caseless and I just don't see a manufacturer switching that kind of thing around because its a completely different reciever assembly - which makes it basically a totally different firearm.
The grenade launcher segment confuses me. If you stop the frame in the right place, the shell says 40mm on it, but it is clearly to narrow for that and much closer resembles a shotgun shell. I could believe it is a high velocity 25mm grenade. The reinforced barrel on that section looks like its for use at range as well, rather than CQB. The whole weapon, including the folding bipod and the long barrel seem to have it geared towards fighting at range.
