Top hipped me to some more info as to why TDP (Technical Data Package) guns work and parts guns don't when pushed hard. LAV (if you don't know who that is, you don't belong on my blog. Go away) is, as far as I know, the one who coined this term: tolerance stack.
Tolerance stack can probably be best defined in a comparison. Guns made to the TDP, or as close as can be, don't have it. The guns are made to the blueprints, so the parts are made to a specific spec and of specific materials. Parts guns don't have that. So, when you use a commercial spec receiever with a different brand of parts kit and whatever other parts, you're creating tolerance stack. Say your receiver doesn't exactly work completely and totally as it should with the parts kit. That's one little piece of the tolerance stack. Add the cheapest BCG you can get. Non-MPI'd bolt, unknown brand of pins. Every one of those CAN add to the tolerance stack. Eventually, all these things add up, and the result is the TS. Push the gun hard, as in a thousand rounds a day in a class over a few days, and you'll see failures. It happens with non-Mil Spec factory guns. Its definitely gonna happen with a parts gun made by somebody who doesn't build guns for a living. Its a statistical fact.
What can be done about it? Not much. Get a gun made with, or as close as can be, to the TDP. That means Colt, FN (good luck finding one) or LMT. That probably means Noveske and a few others, too. Fact is, the commercial tier three guns are probably going to fail when pushed hard. It may not, but tolerance stack is why they do. Check out what LAV, Pat Rogers, and others of that ilk have to say about how those guns perform. They'll almost all say that the Colt 6920 is where its at. When the gun has to run, they're just not all that expensive. If you can't float what the Colt costs, LMT can be had for a little less than a grand. Its pretty clear, with some study and research, that the commercial guns are OK for casual use, but aren't going to stand up to heavy use. I don't wanna hear it either, cuz I don't have $1300 to put into a rifle, but facts is facts.
2 years ago