I have two AR's and am going to start stock piling repair parts for the long haul. I have a gut feeling our next pres may be a democrate so I am starting now. Are extra barrels needed? Do you buy these repair kits (pricey) or by the piece?
I have 4 ARs so I keep 2 barrel assemblys and 8 of every other part except carriers,telestocks,buffers,rear sight assemblies 4,4 M4 handguards gives 8 sectional replacements.and pistol grips.
I buy my spare parts by the piece, but I buy sort of in bulk or with other orders.
If you're really worried about legislation, it's probably a good idea to sock away, say, at least 2 complete lower parts kits plus several extra of each spring, tiny part, and thing that can break outright or wear quickly (like the boltcatch, buffer detent, or firing pin retaining pin), a gas tube or two, and perhaps even a spare set of furniture (you never know, they might ban that, too). Add a spare bolt carrier group and a couple of bolts to that, of course.
If you can find decent deals on a spare barrel or two, perhaps on the EE, then they might be a nice thing to have, but if you're just going to pay retail then the money might better be spent on ammo.
And also -- Tools! Armorers wrench, roll pin punches. You want them on hand. And a giant heap of magazines, one of the most important and ban-prone "spare parts" there is.
It isn't just parts breakage that may be a problem, it's losing the damn tiny-ass parts while your replacing or handling them. Look how many people lose their buffer detent springs.
Lastly, if you're worried about a ban, get a stripped lower or two. You could probably trade them for a lot of USGI mags if another ban came around.
OK, good mags first.
Two firing pin retaining pins and a firing pin, right now. You may bust one while you test all of your magazines. Bad mags are no good.
A spare charging handle. I saw one get stepped on at a lunch break and deadlined a 2,000 dollar rifle until the armorer could order up a new one.
A stripped lower or two while they're cheap. Those can be made into complete rifles in a hurry with the remainder of your parts stockpile if the Rainy Decade hits.
A complete upper, and go with a configuration other than what's on your rifle for variety. I wouldn't buy a fixed-carry handle upper.
A complete bolt carrier beyond that.
One of everything in the lower. The buffer and spring hardly ever go bad, but again, you may need to produce a second rifle on short notice. I DID break a buffer tube at Fort Benning in 1999, so it's not unheard of.
The average civilian owner/operator is not going to smoke out a barrel but it could happen. Again, unless you want to get into armoring, a complete upper of reasonable quality can be had for less than a premium-grade barrel.