I want to start off by talking about a moment at a class from several years ago. it was a cold Thursday afternoon in October, and I was standing over my rifle as it lay in the dirt. We were between drills and I was growing increasingly frustrated at its failure to feed malfunctions. It was at this point that the school's resident weapons guy strolled up behind me to look it over. Now, the primary cause of my issue was lubrication, but that's not the point of the story. The instructor, Scott, turned back to the rest of the class to give his thoughts on "spare parts." The best spare part you can have, he said, is another rifle. But barring that, each of us should plan to have a spare complete bolt carrier group and lower parts kit for each rifle, and we should keep it with us. Related Links * Minimum Capable Carbine * Back to Basics Summary I've noticed a trend during 2020 where the kinds of "gun stuff" that's getting very difficult to come by are complete firearms and ammunition. I think this stems from most of the panic buying coming from new shooters who don't quite know what else they need to look out for. On the other hand, I can still readily find important spare parts like bolts, springs, detents, and even magazines. In an uncertain future, where we don't know when complete AR-15s will come back to the shelves (if ever), I think it's important to start thinking about how we keep our gear "in the game" for the long haul. That means keeping items on hand that we're going to need for routine maintenance. Back to Scott Of course we can all build up a stash of individual spare parts, and we probably should. What stood out to me about Scott's advice that day was the practicality behind it. He was thinking operationally. Should you be in the middle of a match, range trip, or community patrol (if it comes to it) and your rifle goes down with a broken bolt or some other breakage, it's far easier to remove and replace the complete bolt carrier group. The alternative is field stripping the bolt, or carrier, and fiddling with small parts you might lose in the field. Who knows how long that would take while you are otherwise on the clock. Of course, complete bolt carrier groups can get relatively expensive. So it's fine to break it down into the constituent parts.  * Bolt * Extractor * Extractor spring * Gas rings * Cam pin * Firing pin * Firing pin retaining pin * Gas key * Bolt carrier Lower Parts As for the lower, there are a lot of little springs and detents. The most important, in my opinion, is the trigger springs and buffer spring (as well as the retaining pin for when you inevitably lose it).  It's ideal to keep a whole lower parts kit around, though. Just in case. But what about... Two more items on my list. First, consider keeping a few spare barrels around. Yes, I'm aware that I'm advocating enough spare parts to build more rifles if you wanted.