So we tried (and tried) to get enemy carried weapons to reflect their proper attachments, but a bug in the system prevented it from working. It seems that they display as Ubi set them regardless of what you do.
Which brings us to muzzle breaks - indeed it seems that the MODELS for the muzzle break exists, but like everything in Far Cry there are multiple files necessary to create any thing (and hence why to this day I still hadn't created any completely new attachments whole cloth - I'm quite envious of Ziggy's numerous weapon attachments. He is the defacto Far Cry weapons guru)
So we need a muzzle part archetype file which does exits (huzzah!) Archetype 7703373589865.ark.fcb aka FC3/M93_MuzzleBreak. This can be found and examined using the entity archetype browser.
The Z93 weapons property file itself (7671716477238.ark.fcb) would need to be adjusted so that the muzzlebreak was a valid possible attachment. I see a suspicious spot right under the silencer that looks like it might be blanked out (line 1211 - 1267) more than likely this is the area used by the NPC version so comparing the two files would be necessary. If not then a whole new section like this would have to be added to the file. I confess this isn't something I have tried to ever do and it's all "working theory"
But wait! We're not done yet! Muzzle break would have to be added to the shop file (and that definitely WILL require a new section because there is not a pre-existing one which was just disabled unlike most of the existing attachments - Ubi kindly had them in the file for me I just needed to re-enable them. Think I had to add one or two but as I recall it was pretty straightforward cut and paste type stuff.) Again this is uncharted territory because the existing attachment TYPES all have a number associated with them. I can't get to a copy of the shop file right at the moment but for example Red Dot sites are type 66 and Optical are type 67 and so on. This is a little tricky because no weapons have a muzzle break and using the silencer number is no good (since it's for the silencer object). I'm not sure specifically what needs to be done here but I have apprehension that this goes back to trying to add new weapons and lacking a spare ID number - a problem I had with adding the new bows and even just adding back the ACE.
Finally (really? I'm not sure tbh, but lets hope so) there is a file that escapes my memory which handles all of the UI placement for attachments in the menu. There's a good chance that the new attachment won't show in the weapon swapping menus unless you do some copy and paste of the silencers UI image. I'm guessing the HUD lacks an actual muzzle break icon bit as it didn't make it to even the "designed but hidden the from shop" stage :/
Whew. Yeah. So not for the faint of heart. It can be done (clearly). Ziggys done it many times over in Far Cry 3, but I've not tried it yet in Far Cry 4. For good reason (cause it's hard!)
And all this science, I don't understand... It's just my job, five days a week