Okay,

So after owning ARs for a years. I finally intend to purchase a set of spare parts for my current AR. I tried searching as I am very aware that this is a topic that is very much talked about. But unfortunately my search function is not working, nor are my google searches directing me to the specific thread in this forum that show up in google searches.

What are the parts most likely to fail? I know many people mention gas rings, and a LPK of springs. Some people mention bolts (even though I can't imagine mine cracking).

I do have a Geissele SSA trigger installed in my AR, so I imagine I would have to contact them for spare springs? If I did want a new bolt, how would I go about purchasing one? Don't they need to confirm proper headspacing?  

How many do you have?  3 or more, You already have spare rifles.  I keep a few sets of gas rings and some "oops" kits with springs and what not, and essentially enough parts on hand to build an entire rifle.

Thanks for reminding me OP, I need to get another upper coming.

I would want a complete Bolt Carrier Group and a replacement trigger group beyond simply a replacement set of springs. Deeper then that maybe a gas tube and roll pin.

As for checking headspace on bolt a set of gauges could be purchased but lots of folks around likely have a set that would help you out. You’ll probably have several say they don’t bother myself I look at it as it’s to easy not to.

Nope I sold my previous ARs. So currently I only have one.

So I do need a true spare parts set from scratch.

I'd say you basically need a second rifle.

Hmm. I might actually spring for an additional BCG, LPK, bunch of extra gas rings, extractor springs, rings, and firing pin retaining pins, as well as a gas tube and roll pin.

Any word on Nickel Boron BCGs? Are they worth it, or should I just get a milsec BCM BCG?

Slim pickins on BCGs right now.  Any reputable brand in milspec format should do, but if you can only find NIB, that works well too.

DISCUSSION LINK

At minimum.

NiB is brittle and any imperfections in the coating will eventually result in peeling or complete catastrophic failure. My opinion so your milage may vary but M. Phosphate is good and chrome is great. DLC is fine too but expensive for what it is. People love to overthink this, it's easy to do.

If we're talking backups to provide replacement parts for one rifle in desperate times.. at least one new complete bolt would be good to have. As well as a replacement extractor, extractor spring, a good amount of gas rings, an extra firing pin, spare FCG springs, replacement buffer pad and rollpin, and a couple barrels. Magazines with good springs are a must as well. Action springs can wear out. Tubbs flatware magazine and action springs will last over your lifetime.

Having backup rifles is also not a bad idea so you have a ready replacement, will allow you to repair breakages later and not die as your trying to replace the bolt in your carrier.

Sounds extensive, but reasonable. Now that Biden is taking office, I'm taking spare equipment seriously. In the past, it was something I always put off until "when I remember to get to it." So I just now ordered an extra firing pin, 3 new firing pin retaining pins, 2 sets of gas rings, and a new gas tube/roll pin.

How do I go about buying a new Bolt? Will any BCM bolt do? I can still check headspacing at home, but will a new bolt work in an existing Bolt Carrier, or do they need to be manufactured together? I'm pretty sure my BCG is the one that came with my Colt 6920 complete upper. I could just bite the bullet and buy a whole BCG, but I'm not sure I want to do that yet. If I buy the bolt alone, can I buy the rest of the Bolt Carrier later if I choose? Should my extractor also be made by the same manufacturer as the bolt I purchase?

Any bolt should work in any carrier. Change the cam pin when changing the bolt if replacing a used bolt.

I am pretty fanatical about having spare parts.

My view is basically a spare of every moving part, spring, detents, roll pins, BCG/CH, spare gas rings, extractor, etc.

Plus multiples of those!