they should do it like in real life:
to make a gun (or disassemble a gun), you need to have the Manual for this gun on you, and a Receiver (there could be a choice of customized receivers, but they're all compatible with the Manual)
Now, all you need Barrel, Bolt Group, Bolt Cover (or upper receiver, it's almost the same shit), and a Trigger Group. optionally you can put handguards, grips, stocks, sights - naturally they must all be compatible with the Receiver...
some of the options could be only enabled by having the receiver with the side mount, like AK rifles, or the bolt cover with scope rings
the best thing is a typical player doesnt have to know what the hell it all means and how to put it together - if he doesnt want to repair his 20% bolt group, he can just take the gun to in-game gunsmith and he'd just say what's wrong and how much it costs to fix... BUT if he wants to customize, or not to pay gunsmith the service charge, he can invest in his gunsmitting skill and do all the work himself (since Manuals have min. skill reqs to be usable)
while FO3 will probably not go into the extreme detail and keep the details simple (prolly only have the receiver, barrel, and an optional mount), i know a lot of modders whod appreciate this kind of modular flexibility
to make a gun (or disassemble a gun), you need to have the Manual for this gun on you, and a Receiver (there could be a choice of customized receivers, but they're all compatible with the Manual)
Now, all you need Barrel, Bolt Group, Bolt Cover (or upper receiver, it's almost the same shit), and a Trigger Group. optionally you can put handguards, grips, stocks, sights - naturally they must all be compatible with the Receiver...
some of the options could be only enabled by having the receiver with the side mount, like AK rifles, or the bolt cover with scope rings
the best thing is a typical player doesnt have to know what the hell it all means and how to put it together - if he doesnt want to repair his 20% bolt group, he can just take the gun to in-game gunsmith and he'd just say what's wrong and how much it costs to fix... BUT if he wants to customize, or not to pay gunsmith the service charge, he can invest in his gunsmitting skill and do all the work himself (since Manuals have min. skill reqs to be usable)
while FO3 will probably not go into the extreme detail and keep the details simple (prolly only have the receiver, barrel, and an optional mount), i know a lot of modders whod appreciate this kind of modular flexibility