I don’t have enough money to buy a BCM 18” but I could possibly save up for an 18” BCM upper to swap out the upper of my Ruger 556 MPR 18”. I heard that the most important parts of an ar-15 are the uppers, BCG, barrel, etc. My MPR already has a custom trigger that came stock on the rifle. I saw a YouTube clip of a gunsmith that specializes in AR’s comparing a BCG of a PSA $400 vs Knights armament $4,000. He said because the machining and geometry of the Knights armament is more precise and the BCG is better quality the wear on it is much less vs the PSA BCG, and I’m assuming the barrel is obviously better on the latter too. If I replace my upper with say, a BCM upper, will that make the rifle more reliable, longer lifespan? Any advice if you don’t have the money for a mid tier AR but can afford swapping parts? Is it worth it?