Like the 10mm Pistol laser sight could be added to any weapon that it could be realistically added to in real life. Like adding the before mentioned laser sight onto..... The Riot Shotgun. Or adding the rifle scope from the hunting rifle onto the Service Rifle. I know that there are weapons like the Marksman Rifle which do the same thing, but this could be like a poor-mans variant. It could be purchased earlier in the game, and could stand in for the sniper rifle, and long range rifles earlier in the story.

Every gun frame and composition is different, as are the mod-types that are engineered for them. A service rifle has a carry-handle on top, and there is no way you could fit the hunting rifle scope on top of that without it being extremely rinky-dink and inaccurate, hence pointless. Similarly, the underside of a shotgun barrel is completely different from the underside of the 10mm pistol, where the laser sight is engineered to fit. Besides, the shotguns already have choke mods, which do exactly the same thing as the laser sight mod does- narrows the projectile spread. Duct-taping the wrong kind of mod onto a weapon it was never made for, just doesn't work very well. While it would be 'nice', I suppose to make the game have universal mods that just magically fit on anything, it would be completely unrealistic and just.... dumb. Glad it is the way it is, myself.

WMX makes some weapon mods working for two or three weapons, i.e. laser recycler working for RCW and both rechargers. Mentioned by you laser sight is also working for more weapons, but in making sense way.

Yeah WMX does almost exactly what the OP said, but within reason. As in the Hunting Rifle Scope is not going to be able to attach to a Service Rifle because the attachments would be completely different, but there is an added mod simply called the Laser Sight that can attach to many different weapons.

It's not as black and white as that Smokey. You can mount rails on shotguns to accept lights, laser, all kinds of stuff. Mounting a scope on a fixed carry handle AR would be a real [censored], as you say, but it would be nice if in the next game a more modular mod (redundancy FTW) system could be implemented. There's no real reason why you shouldn't be able to use the extended mag from the service rifle in the marksman carbine. Unless for some weird ass reason they didn't use standard mags on two military rifles chambered for the exact same round.

-Gunny

In WMX the added mod 5.56mm Carbine Extended Mags does work with both the Service Rifle and the Marksman Carbine.