In that regard, the AR has become the firearms equivalent of the PC, where anybody can bolt anything they want onto it, whereas it was once an Apple, where you got your parts from a single approved source supplier and that was it. Being the PC gun is not all that bad actually, since it has led both to a dramatic fall in price as well as a virtual avalanche of improvements and innovations which even the blessed Saint Eugene of Stoner (Eugene Stoner was the original designer of the AR-15) couldn’t have ever imagined.
The rub lies in the fact that many of these innovative new components and sub assemblies work perfectly when installed as a complete unit but may display occasional maddening glitches if they are mix-and-matched with parts from another system or manufacturer. Looking at the AR-15 trigger group or, on a wider basis, the full lower parts kit is one of the first places to start when you are having problems with the gun (okay, “rifle” for those of you who are or were Army or Marines).
Mismatched parts can create a lot of headaches, but perhaps none so dangerous as when they cause failures in the sequence which the disconnector and hammer engage and disengage. This can lead to slam fires– followed shortly thereafter by a barrel blowing up in your face while you imagine yourself to be the proud owner of a secret full auto rock-and-roller. This is one of the reasons why Mil-Spec parts are so important. A standardized manufacturing process that is focused on meeting or exceeding Mil-Spec helps reduce or eliminate issues.
The moral of the story is that you need to replace entire assemblies on an AR rather than swap out the occasional worn part. Since these guns see a lot of ammo put through them, they tend to exhibit more rapid wear factors than you might find on your old 30-40 Krag, which can last a couple of centuries before it needs new parts. Rapid wear can also be aggravated by the use of no-name parts which may not be properly heat-treated to the correct engineering standard.
Find yourself a reliable manufacturer that has been in business long enough to prove that they haven’t been sued into oblivion for selling defective merchandise, then purchase the items you need in complete and factory-matched groups. Pick up an entire AR-15 trigger group rather than replacing that worn-out hammer. Spend the extra few bucks on a complete lower parts kit and swap everything out rather than chase failure-to-feed gremlins one part at a time. The chances are good that you’ll end up with a more reliable and much safer weapon, not to mention that you can spend time out on the range with an operational firearm rather than tearing your hair trying to figure out what’s wrong with the one you’ve got in pieces on your kitchen table.