I consider a build putting together an entire rifle from individual parts wich to me is a stripped upper,stripped lower and the assembling all the diferent parts assemblies on those 2 items.If I change out a barrel im re-barreling,changing parts are a reapir,upgrade.If I have to take a machine tool of some kind to the rifle or parts its a modification.If its a stripped upper or lower its partly built or ive done an upper or lower build.
cutting,threading or shaping is a modification or a step in making a part for a build.
Orange county choppers builds custom bikes from existing assemblies...cutting,threading or shaping is custom fabrication wich they also do.They dont build engines from scratch,they may custom fabricate parts but some things they use are already ready to use.If you are cutting,threading or shaping id call that a "custom fabricated"build.
Besides semi-auto rifles in them selves require custom fabrication especialy for fire control group parts.To me to build or assemble is one in the same.If you cut,thread or shape its a scratch build or custom fabrication,as ive said some parts have already benn cut or threaded before you buy the assembly.So if I machine full-auto parts to semi standard myself and add a coat of krylon to the rifle thats a build but its not if the factory or machine shop did it before I assembled it?
The reason why the tail end of a disconector is shiny is because it was a full-auto part with the tail machined off or cut off for semi-auto only.They just dont forge or make semi-auto parts they are made 1 way and then machined or cut down to semi-auto standard and thats I guess a fabricated or custom part thats machined to a certain standard.Just because you didnt anodize the receivers does not mean its not a build..its just not a "custom"build.and even custom builds have standard assemblies.