I really want this. I've been a lurker on here for 10+ years, finally have some resources to maybe start building some stuff for myself. I do Art for film and commercials so I have a bit of experience. I usually PD/Art Direct so I rarely get to be hands on anymore, but I've built a few props from scratch for work before. I've not really done anything significant out of aluminum though.
I think the spool below the barrel is from a swingarm spool if they went the found parts route. Something similar to this:
Amazon - Vortex SP209S Swingarm Spacer
But I'm thinking this is scratch built like Joatrash FX said. It doesn't make any sense when you could easily cnc almost the entire blaster.
Pretty sure the torx machine screws are standard 8-32. Probably 3/8 and 1/4 lengths.
I also feel like the grip section doesn't continue inside the chamber section. I feel like the grip bolts onto the inside of the rear plate of the chamber.
The main structure of the grip section is just a hair over 3 times the thickness of the sandwiched outer plates. The outer plates appear to be the same thickness as the sides, front and back of the chamber. As do the rounded upper and lower pieces of the chamber.
Based on all that, I'm guessing the barrel has a 1-1/16 in OD as the chamber is slightly wider (say 1-1/4 OD)
I think they just modified the stock mauser grips and than made casts based on the double screw mod. Found a few stock grips that have the same number of ridges and the flare.
Sorry for the word vomit.