Now, I'm not saying that all AR-15 manufacturers make all their components, but I'm not saying that all of them buy from the same company, nor that they buy the same parts from said company.
I've looked at 4 manufacturers websites, for 4 comparable rifle, all roughly within the same price range, to see what specs they list for their rifles.
Rock River Arms
What you will notice from these links, is that RRA and Bushy barely list any of the specs for their rifles. DPMS lists some things, but not everything. Spike's on the other hand, lists nearly everything. All the materials, Q&A processes, coatings, all the way down to little things like the coating on the firing pin retaining pin.
Now, if all of these companies do use the same parts and processes, why do the others not show it? If Company A's parts are as good as Company B's, then Company B should show specs like Company A does.
What I find the most humorous, is lots of guys talk about how most people can't afford this gun or that gun, can't afford a gun with this part or that coating, but guess what? The Spike's, which shows ALL the specs, and in my opinion is a higher quality rifle, is the cheapest of all 4, and comes with a LIFETIME WARRANTY. Now that is building a product you're proud of and standing behind it.
If DPMS, Bushmaster and RRAs rifles have a BCG that is made from the same steel, has the same coating and went through the same testing a QA, then why don't they show it to their customers? Spike's does. If the barrel has the same MPI and HPT done to each barrel, not just batch tested, then why don't they show it? Spike's Does. Is their front sight base designed to be used with a flattop upper? I don't know because they don't tell you. Spike's does.
See what I'm getting at here? Spike's is my manufacturer of choice. When I buy a Spike's rifle, I know EXACTLY what I'm getting. I know the quality checks that went into it. I know all the testing processes that were done to the various parts. I know what type of fasteners were used to secure the gas key. I know the coatings on various parts of the rifle. And to top it all off, I'm paying less for a rifle with full disclosure on the parts and processes used than I would if I bought one of the other company's rifles built with mostly mystery parts.
Spike's isn't the only manufacturer that does this. Most of the other high end manufacturers do the same thing. I'm pressed for time or I would've posted links to them as well.
You can say "parts are parts are parts are parts" all you want. But when I want to know what parts I've got, the coatings on them and the tests they went through, I need only look on my rifle's manufacturers website. Those of you with a DPMS, Bushmaster or RRA, well, you guys just keep saying to yourself "parts are parts".