I found some pictures of weird looking Avatar used props, I know that in australlia they were unable to use the balnk firing models, so they used foam / rubber ones, here are some pics of them:
A unique example of a GS-221: Note that the slite in the back is longer and wider and that the Mini-14's charging handle wasn't removed, and replaced with a screw, like in the other props I don't know if there is also the PDW with this type of 'shell', If someone knows, please tell me Why did they do this one diffrently? I found the picture on a chinease site here's the link:
*4カスタ*工房 *画に出てくるカスタ*銃
A foam GS-221, that looks very much like the EURYS II in Avatar:L The Game by Ubisoft

M-60 foam props