I would have thought the Colonial Marines Technical Manual by Lee Brimmicombe-Wood would be a good place to start... and then there's the M41-A Manual by Derrick Baena. Most of what you're after should be covered in those two publications.
I own a physical real copy of the tech manual. It's out of print, though. I actually downloaded a PDF and JPG version of the manual just to have. I'd send them to you but they are over 50MB each. If you do some creative searching you might be able to find it out there. I tried to look for a good link, but I got nothing but spam. I used to have a copy of Derrick Baena's manual too but included it with my SD Studios Pulse Rifle when I sold it. Does he still make/sell these?
Good luck.
I believe Armat is the fictional company that makes it.
I had one of the USCM Technical Manuals once. It has a wealth of information within but it was too much 'fluff' for my personal tastes. The last one I priced was being offered for around $200 on amazon. The Derrick Baena Pulse Rifle field manual is much more prop specific and well worth the money if you can still find one. Mine is personalized and I could not ever see parting with it.