The way I parts-select and assemble an AR today is so different compared to what I did 20 years ago, it literally feels like working on a different gun. You could hand me the same parts in 2000 and the same parts today, and I would approach it so differently, if I were to make 2 separate videos of those processes, you would see what I mean.
Along the way, I’ve acquired more tools specific to the AR, or made my own.
One of the tools that sticks out the most is the receiver face lapping tool. Anodizing thickness varies on the faces, even though the machining is square. The anodized surface needs to be made square again on some receivers, though I’m seeing more and more that are square from the package.
The most important components in a build are the barrel, followed by the bolt, then the carrier, carrier parts, and receivers, then the gas block.
The critical things I look at on the barrel are:
Chamber dimensions-do they fit a fully-seated factory cartridge and my dummy rounds, then allow the cartridges to drop-free with gravity, or come out with a small tap in my hand? I’m basically checking to see if SAAMI spec COLs with common loads jam the lands or not. Jamming the lands is a bad condition to have in a gas gun.
I then check the gas port to make sure it’s an optimal diameter for what I’m doing. I see a lot of oversize gas ports in 5.56 and 6.5 Grendel, usually ports bigger than .076” at MLGS on both. A 5.56 MLGS .094” port even at 14.5” will recoil hard and break weaker optics in short order. A 14.5” MLGS with .076” runs like a pussycat, very easy to control.
There are a lot of after-market 18” and 16” “Grendel” barrels with .094” gas ports at MLGS and even CLGS on the 16” guns. The cyclic rate is way out of control on them as a result, with early unlocking, trashing the brass, don’t run well. With a .076” port MLGS on both 16” and 18”, they run like pussycats.
Muzzle threads need to be square and concentric to the bore if you care about accuracy and/or are going to suppress.
Barrel extension index pin needs to be press-fit into the extension without being canted or drilled into the barrel tennon threads. Some barrel makers like to drill into the barrel tennon, which is not in the TDP. If they control the process tightly with a staff who holds themselves to higher standards than seem capable of most current workers and leadership, then they can be done ok that way. As soon as they drill too deep, they just compromised the chamber walls. Have seen it where upon firing, the brass comes out with weird round marks right at that location down on the case body. The brass is actually pushing the steel chamber wall outwards and leaving huge circular extrusions. Some like that will FTExtract due to the added case adhesion to the walls.
Bolts: I can already see this will be too long-winded, so I’m going to bed. Sorry for the derail if all you were looking for was assembly instructions. Zeideker’s book is excellent on the matter. There are some great videos from Joe Carlos from the AMU worth watching. It will feel like he’s not even talking about the AR-15, compared to most of what else is out there.
If you just want to slap parts together and have something that looks like an AR-15, there are thousands of videos done by amateurs who have been at it for a few years, and now think themselves as experts. Then there are guys who have been at it for 20-40years who recognize that they are still learning new things all the time. I am one of and listen to the latter group.
Check out InstructorChad’s videos on gauging. That will fast-forward you past all the amateurs and much closer to the latter group of builders.