Maybe in brand and materials, but whatever you heard either was entirely unclear so that you could not understand or was just flat out wrong. Armalites all use version 2 mechboxes. Minus the armalite PTW but thats a diffrent story and the semi unreliable madbull co2 mechbox. If theres a diffrence in gears its probly brand or materials, but its all the same design.
That shim lay out linked is a decent pic, but every shimming experience is diffrent, when we reshimmed my 416, it looked nothing like that set up at all.
Since 2 of the systema bushings I had did not sit flush in the mechbox.
"Its only a little bit on fire"