What this means to me, and here we go again, is when someone makes the statement "I want to keep my Garand/Carbine/03 just as I received it because ..........".
In the course of 60+ years, whether just behind the front lines, in an Army, USMC, Navy, Coast Guard, ROTC armory, or a Reserve Unit, parts got swapped around all kind of ways.
They grabbed a part, installed it, if it went "Click - BOOM", it was the CORRECT part.
I know not what course others may take, but as for me, give me ----- the ability to swap parts around on my weapons as I see fit. If I have an SA, I want to put SA parts on it. If I have an HRA, I put HRA parts on it.
As long as it fits and goes CLICK....