The problem with Frankenguns: why parts guns fail under hard use

I recently had an online conversation with a very experienced shooter regarding his thoughts as to why "parts guns" fail in tactical carbine classes. This individual shoots 2-5 classes a year on his own dime. That doesn't count SWAT training, instructor classes, patrol rifle classes, in services, and other training he gets from his job in law enforcement. He shoots A LOT, under pressure. I trust his opinion. Here's the gist of what he theorized is the reason that parts guns, and factory guns from "tier two" manufacturers ( the commercial AR's on the market that are widely distributed) fail in hard use.

There are people all over the net arguing that their Bushmaster/Rock River/DPMS/stripped lower parts gun is "just as good" as the Kool Aid Brands. Here's why they're not: Mil Spec doesn't just mean parts interchangeability. It means "as spec'd by the government". Only suppliers to the government (Colt, LMT and FN) get a very expensive document called the Technical Data Package (TDP). These are the exact blue prints for a given model. What is suspected to happen with other brands is that they have obtained a gun that they believe to be in spec, and they reverse engineer the rifle to make their version. They're not making the guns off of the TDP; if they were, there'd be no such thing as a commercial spec receiver extension (buffer tube).

Its entirely possible for a rifle that's been built from parts from many different sources to run like a champ. That's unusual, in terms of hard use. A rifle may be able to shoot five thousand rounds per year with no problems. However, take that same rifle and subject it to a five day carbine course where you may shoot a thousand rounds a day, and you're subjecting it to much, much more stress. This is where rifles fail, and the parts breakage can't be narrowed to just one part or set of parts. Everything has been seen to break in classes if you've seen enough of them. This is exactly what the more high volume trainers will tell you; they've been saying it in classes, interviews, and magazine articles for years. For whatever reason, shooters have not been listening. They keep saying "My Brand Whatever rifle is every bit as good as" or "just as good as" or "the same thing cheaper as" the true Mil Spec guns are. The simple fact is, there is no proof for this. How many times do you need to see different pictures of "Brand Whatever" bolts that are broken before its enough? How many spring sets or pins or hammers or gas tubes and carrier keys coming loose have to be shown before the truth becomes obvious?

Here's the bottom line: if you really want a gun to stand up and run, you increase your chances DRAMATICALLY by going with a true Mil Spec gun. Sure, a Colt is hard to find and expensive. They seem to run at least $1200. LMT's are typically a bit more...but oh, so worth it. If I had an LMT to put up against Schwaggie, the difference would be striking. Cycle the bolt on an LMT. Then do the same thing to a commercial AR. You'll feel a very, very big difference in smoothness. Why is that? Blueprints. Yeah, it matters.