AR Assembly QC Advice

[ViperTwoSix]

Hello,

I am looking for advice/input on what things I should do during the assembly of my AR to help ensure the reliability and/or durability of the weapon.

I don’t intend on storming the beaches of Normandy, Not conducting any extreme torture testing, but would like to be able to trust that it will go bang when I pull the trigger and serve its purpose if it ever came down to a defensive situation.

I know there is a lot that goes into it, and there is a lot I don’t know, and that I will never be as good as a top tier weapon from someone doing this for 20 years. My goal is to hopefully assemble with quality in the middle of “you’ll never be as good as Colt/SOLGW/DD/LMT/etc.” and “Much better than a PSA/Radical/etc.”

Please refrain from replies such as, “buy a complete upper from [insert favorite mfg here].” I have already committed to doing the build for the knowledge and experience. Also, please refrain from a general reply such as “buy quality parts” unless you have a specific reason like “use XYZ part instead of ABC part because....” I realize quality parts matter and there are plenty of threads on what constitutes a quality manufacturer of parts. I am more looking for specifics on what I should do to ensure I am building a quality reliable weapon. I am fully aware that there are some learnings involved, but I am hoping to learn as many tips, tricks, do’s and don’ts As I can before actually making a mistake and having to do it over.

I have a list (in no particular order) of things I have seen or read and am hoping you all can share your knowledge and experience, look it over, tell me if something should not be done and why, and if there is something in addition that I should do and why.

Sorry for the long post, and thank you in advance for any advice!

The list of home-build QC:

Conduct appropriate function checks (trigger and hammer function, safety selector function, mag catch, bolt catch, etc.)
Verify hammer spring correctly engages hammer pin and trigger pin
Season castle nut threads- hand tighten on/off 3x
Aeroshell castle nut threads
Torque castle nut to spec
Stake castle nut
Torque gas block set screws to 25in.lbs
Red loctite gas block set screws
Blue loctite grip screw
Blue Loctite handguard screws
Torque handguard screws to mfg spec
Season barrel nut- hand tighten on/off 3x
Aeroshell barrel extension
Aeroshell barrel nut
Torque barrel nut to mfg spec
Verify headspace with go/no go gauges
Verify feed ramp alignment
Check feed ramp for hang ups or overhang
Verify extractor o-ring
Test bolt gas rings with bolt/carrier drop test
Check gas tube/gas key alignment with carrier drop test
Verify gas port alignment?
Gauge firing pin protrusion?
Gauge gas tube/gas key?
Torque muzzle device to 20-30 ft.lbs per mfg spec
Lube all springs, detents, and internal components during assembly


Also, if there are other threads that discuss this please feel free to post the link and point me in the right direction. I did (and still am) searching threads but I’ve seen a lot of generalizations like “build it the right way” but not a lot of specifics on what that means exactly.

Thanks again.

[mmc45414]

I also think a gas block should be at least dimpled. That way you also know it is in the right position.

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[MistWolf]

Welcome to the forum! This a good place for no nonsense info on firearms, shooting and enabling the revolver fetish- and chainsaws. Can't forget about the chainsaws.

First, you need to let the following go and never say or think it again.

I don’t intend on storming the beaches of Normandy, Not conducting any extreme torture testing, but would like to be able to trust that it will go bang when I pull the trigger and serve its purpose if it ever came down to a defensive situation.

No one intends to "Storm The Beaches Of Normandy" with their AR, although it makes an interesting "What If-?" question. Usually, when people start off with this, they don't want to seem weird about getting "hardcore" with their weapon of choice. Or worse, "I've made up my mind and want people to validate my choices".

The reality is, to build an AR correctly, it will be built to storm beaches. Anything less impacts reliability and durability. Do you want an AR that will malfunction, wear out quickly, break or loosen up in a self defense situation? Of course not. So, ditch this whole "Not Storming Beaches" thing.

To save space & time, I'm only going to address things on your list that need correction or expanding

Season castle nut threads- hand tighten on/off 3x
Aeroshell castle nut threads

Not needed. Torque to spec with threads clean & dry. No grease. No Locktite. Be careful when staking. Over staking will damage the threads of the receiver extension.

Torque gas block set screws to 25in.lbs
Red loctite gas block set screws

I'm not certain about the torque spec. I tighten the set screws by feel, but I've been an aviation technician for more years than I care to admit and have experience. Dimple the barrel for the set screws. Use the toothed set screws sold by Forward Control Designs and stake the set screws in place. Don't use red Locktite unless you want to have to drill out the set screws to remove them. The receptacles of head head screws are very easy to strip out.

Verify extractor o-ring

No O-ring. If an extractor spring needs an O-ring to function reliably in an AR of any barrel length, it needs to be replaced with either a Colt or Sprinco extractor spring. The O-ring was a temporary fix, needed only because the military wouldn't add the correct Colt spring to the supply system. That situation has been since rectified.

There are only two extractor springs I use for a standard AR bolt-
-Colt copper colored with black insert
-Sprinco with black insert

Add the following to your list-
- Quality springs. Firearms are only as good as the springs. The Big Three are extractor spring, hammer spring and action spring. Pay particular attention to the extractor spring. Once again, Colt or Sprinco, in that order of preference.
- Proper gas port. Starting with the right size gas port ensures a large number of problems are eliminated at the start.
- Proper buffer. Contrary to Internet Lore, buffers for the 5.56 is simple. Buffers that work are the H2, A5H2 and Rifle, used with the appropriate receiver extension and spring. H buffers are good, but the H2, A5H2 and Rifle buffers are better. Carbine weight buffers are too light. Tungsten powder buffers are less effective.
- Over/under gassing cannot be fixed by changing buffers and/or springs. Period. Trying to fix gas drive problems with a buffer is like taking aspirin for a cut. It may dull the pain but the bleeding continues.
- Stay away from underpowered ammo. An AR properly tuned for 5.56 ammo becomes under gassed when using underpowered ammo. Using under powered ammo is like restricting the air & fuel to an engine and wondering why the car can't get out of its own way.
- Do not use the "Ejection Chart" to determine how an AR is gassed. However, if the ejection pattern is too far forward, install a new Colt or Sprinco extractor spring.
- Get the right tools. They'll save you time and headaches. Do not ever use Vice Grips to assemble ARs.

[HCM]

Mistwolf is spot on with this:

First, you need to let the following go and never say or think it again.

Quote Originally Posted by ViperTwoSix View Post
I don’t intend on storming the beaches of Normandy, Not conducting any extreme torture testing, but would like to be able to trust that it will go bang when I pull the trigger and serve its purpose if it ever came down to a defensive situation.

You either have a piece of Life-Safety equipment or you don't. Nothing wrong with fun/range guns but it's kind of like the way you can't be "half pregnant."

Most AR's, even craptastic ones, can likely get through the mag or two which might be fired in an actual incident. The two issues with substandard AR's are: 1) "It's not the odds, it's the stakes" and 2) durability at high rounds counts is about holding up to the firing schedule needed to develop and maintain proficiency rather than holding up to end use. One thing to keep in mind on PF is it's mission statement is "for students and teachers of the pistol" meaning it is a technical shooting/shooters forum rather than a "gun" forum.

Re: building an AR, are you mechanically inclined ? i.e. Do something mechanical for work or the type to rebuild your own lawn mower motor ? If yes, then you can likely build a solid AR off internet advice with quality parts and some specialized tools.

If you are not mechanically inclined you can still do it but an AR armorers course will be worth every penny.

[ViperTwoSix]

Thank you MistWolf and HCM on the advice on my comments about the intent... what you say makes a lot of sense. Also, thank you for the awesome advice!

Regarding being mechanically inclined, I have done a few basics like repair a lawn mower, replace basic car parts (oil, fluids, headlights, spark plugs), done some basic electrical work, basically house-hold projects. Either way, an armorers course would be very beneficial. Thanks for the advice!

Any thoughts on using the USMC M-16 Maintenance Manual (TM 05538/10012-IN) as a guide? I was able to get a copy of it but it’s dated 2008 and I’m not sure if there is anything newer/better.

[HCM]

Thank you MistWolf and HCM on the advice on my comments about the intent... what you say makes a lot of sense. Also, thank you for the awesome advice!

Regarding being mechanically inclined, I have done a few basics like repair a lawn mower, replace basic car parts (oil, fluids, headlights, spark plugs), done some basic electrical work, basically house-hold projects. Either way, an armorers course would be very beneficial. Thanks for the advice!

Any thoughts on using the USMC M-16 Maintenance Manual (TM 05538/10012-IN) as a guide? I was able to get a copy of it but it’s dated 2008 and I’m not sure if there is anything newer/better.

If you are building a 20' rifle sure. There are differences between the M16 and the M4, such as gas system, dwell time, extractor spring etc.

The whole O ring and extractor spring insert thing were developed to address reliability issues caused by running certain M16 parts in M4s.

[Darth_Uno]

I also think a gas block should be at least dimpled. That way you also know it is in the right position.

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I've looked into this when I started building more on my own and opinions vary, even straight from the source. Some say you definitely need to dimple, some say you only need loctite or Rocksett, some say you need both; Odinworks and Aero (BA barrels) say you don't need anything.

Some of mine are dimpled and some aren't. I've yet to have one rotate or walk up. I'd still recommend it for anything halfway serious, especially if you shoot suppressed. If you don't own a jig and drill press, get a pre-dimpled barrel. Pinning is a little much to go out of your way to do, especially since 99% of gas blocks are under the handrail now.

[Darth_Uno]

I'm not certain about the torque spec. I tighten the set screws by feel, but I've been an aviation technician for more years than I care to admit and have experience.

After nearly 30 years on jobsites, I just go by German specs - gutentight.

Get the right tools. They'll save you time and headaches. Do not ever use Vice Grips to assemble ARs

But they won't save you money. Once you can do whatever you want, it's on now.

[mmc45414]

I also think a gas block should be at least dimpled. That way you also know it is in the right position.

I've looked into this when I started building more on my own and opinions vary...
Some of mine are dimpled and some aren't. I've yet to have one rotate or walk up...

I was always worried about getting the gas block in the right spot, and getting the tube aligned, and not having it move. It seems like dimpling with a jig solves all three problems.
I have only done a couple, but it seems like it is a huge step between hoping and knowing.

If you don't own a jig and drill press, get a pre-dimpled barrel.

IMO dimpling just the one hole below the gas port makes a lotta sense. Gives you all of the alignment upside without locking you into a specific gas block.
I bought two (0.625" & 0.750") of the SLR jigs:
https://slrrifleworks.com/750-dimpling-jig/
and for $32 would plan on getting another one if I didn't have the diameter I needed.
I did NOT use a drill press. I clamped the jig into a vice and let the barrel dangle, and used a simple battery drill. You hardly need to do more than touch off from the initial contact.

Pinning is a little much to go out of your way to do...

Yeah.... pinning seems like a BFD for only a little better, IMO. But I do not ever see doing another one that is not dimpled.

ETA:

Get the right tools.

Yeah, if you are not willing to invest in tools (like dimple jigs) you can still have fun with this, just never grab the thing if you need it.
I look at building just like building a kit car or experimental aircraft, two safety related endeavors I will probably never get around to actually doing. But AR building is a hoot!

[Darth_Uno]

I did NOT use a drill press. I clamped the jig into a vice and let the barrel dangle, and used a simple battery drill. You hardly need to do more than touch off from the initial contact.

That's one of those things that shouldn't be all that difficult but...I'm not gonna tell you to just go at it with a Dewalt.

And yes I've got the Rainier jig. Makes it super easy and idiot (me) proof resistant.