AR Assembly QC

#1
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.

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 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
 
#2
I just rolled in from a 20hr commute from teaching a couple of Armorer courses, so I will try and be coherent with a response.

Looking at your list, it appears that you have been doing some reading in different places, a guess would be different internet forums. Some of things on your list may or may not apply to your build, as the actual parts used will dictate what and how you need to do things.

From your list:
Verify hammer spring correctly engages hammer pin and trigger pin.
The hammer spring has two functions, first it pushes the hammer forward with enough force so when the hammer strikes the firing pin, that the firing pin goes forward into the primer of the ammunition and ignites. The second purpose of a hammer spring is that it's legs sit on top of a groove in the trigger pin, which is how the trigger pin is locked into the receiver. A hammer spring has no engagement with a hammer pin.

Torque gas block set screws to 25in.lbs
There is nothing wrong with torquing the gas block set screws to a specific tension, this will actually be gas block specific, so I would suggest making sure you follow manufacturers guidelines.

Red loctite gas block set screws

Locking the gas block set screws is fine. If you are going to, then I would suggest making sure that the rifle functions correctly, and make sure you run enough rounds through it that you are confident that it runs reliably. Should you have problems with it, and you have thread locked the screws, you may have trouble getting the screws backed out. When we build rifles, we drill and pin all gas blocks, this makes sure that the gas block won't come loose. I would also suggest making sure the gas block is in proper alignment with the gas port on the barrel, we make alignment fixtures for this task.

Blue loctite grip screw

You can thread lock grip screws, but this isn't usually necessary as most grip screws are mounted using the addition of a lock washer. Some grip makers use screws that have a dry thread locker (like Nylok) that are shipped with the grip.

Season barrel nut- hand tighten on/off 3x,, Aeroshell barrel extension, Aeroshell barrel nut

The Milspec is to use molybdenum disulfide grease, which is what we use and teach to use when teaching Armorer courses. Whichever you use, make sure you apply it to the outside of the barrel extension, and threads on the receiver where the barrel nut threads onto the receiver. The purpose of lubricating these areas is to keep the dissimilar metals of the steel barrel nut and aluminum receiver from molecularly bonding under heat.

Torque barrel nut to mfg spec.
If using a free float tube, follow the manufacturers directions, this includes torquing any screws as well like on the Midwest Industries versions.

Verify headspace with go/no go gauges

I would highly recommend gauging headspace to make sure you are meeting the minimum and maximum specs on whatever caliber you are shooting. I have seen a lot of blown up rifles where people just threw parts together and didn't gauge anything, only to find out the hard way that things were out of spec when the rifle blew up. We see a lot of barrels that the headspace is within spec, but there is no free bore in the barrel, which results in a blow up rifle as well, so make sure everything is good to go before shooting it.

Verify extractor o-ring
Some manufacturers don't use them. Some companies like BCM will send them in a bag with their bolts, which gives you the option to add them if you wish.

Gauge firing pin protrusion?
This is caliber specific, so make sure you use the proper specs

Torque muzzle device to 20-30 ft.lbs per mfg spec
Follow the manufacturers specs, it may vary depending upon what type of device and washers or shims are being used.

As for what else to do and what to use, it will depend upon the exact use of the rifle and what parts are being used. So any information that you can provide on what parts you are using would. When teaching Armorer courses we show all sorts of parts (Some good, and some bad), and spend time helping Armorers understand the strengths and weaknesses of the different parts. We also preach in Armorer courses that there three things you need to not skimp on, these are barrels, bolts and triggers, as these are the heart, lung and aorta of the gun and what's under the hood. I would suggest running a bolt that is made of Carpenter 158 steel, that has been shot peened, parkerized, high pressure tested and magnetic particle inspected per Milspec. There are a lot of sub standard bolts and other parts on the market today, and we show lots of examples of these where they don't work or have failed. We see lots of gas keys that are not staked or staked correctly, which allows us to put our Sully staking tools to good use in Armorer courses.

I will add more later



CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123
 
#3
Hi Greg,

Thank you for the reply and great advice! I really appreciate your input. I have been reading a lot of threads, watching various videos, etc. It seems there is a lot of great stuff, but also a lot of the “just buy an upper” and “use quality parts and build it the right way” that I mentioned. Taking an armorers course was also recommended, which I can’t disagree with.

My intended purpose of the rifle would be used primarily for self defense. This is where most folks in other threads have said “buy a proven factory rifle” which I understand completely, it wouldn’t provide the challenge of building it myself. As a note, I am willing to invest in the proper tools, so I’m not planning on just throwing everything together haphazardly.

Below are the parts I was considering, but nothing is set in stone so I am open to advice and suggestions if it looks like something wouldn’t be compatible.

Spikes Tactical Lower
Spikes Tactical LPK
SOLGW Liberty Fighting Trigger
Aero Precision mil-spec buffer tube & spring w/ H buffer weight
Grey Ghost Precision upper
Toolcraft Nitride BCG w/ C-158 bolt
ALG Defense EMR V2 free float rail

Barrel/ gas set ups I was considering:

Rainier Arms 416R SS 16” mid-length gas, 1/8 twist, 5.56 NATO, Rainier Arms low-pro set screw gas block

or

Ballistic Advantage Hansen 4150 CMV 16” mid-length gas, 1/7 twist, 5.56 NATO, Ballistic Advantage low-pro pinned gas block

Also, I know I am full of questions, but would there any benefit to using a Sprinco blue extra power action spring over the standard carbine spring?

Thanks again!
 
#4
Hi Greg,

My intended purpose of the rifle would be used primarily for self defense. This is where most folks in other threads have said “buy a proven factory rifle” which I understand completely, it wouldn’t provide the challenge of building it myself. As a note, I am willing to invest in the proper tools, so I’m not planning on just throwing everything together haphazardly.
!
Problem is, you don't know what you don't know. I'm now in my 3rd decade of wrenching on AR's and have multiple certs under my belt (including Sully's) and I've never stopped learning. I'm only now to the point where I can spec, build, and assess a complete gun that I'd trust my life on....and that's mostly because other people smarter than me have done some of the heavy lifting in knowing how critical parts/components interface and tolerance stack.

Assembling your own AR is awesome, but don't be too quick to have it be a "defense" gun that has a lot riding on it. Much like, would you rather have the first helicopter ride be in something you cobbled together from a kit or something that came from Bell?

I'm pretty sure no one here can honestly say: "Yep, my first AR build went smooth as silk and I totally would do it 100% the same way today."
 
#5
Problem is, you don't know what you don't know. I'm now in my 3rd decade of wrenching on AR's and have multiple certs under my belt (including Sully's) and I've never stopped learning. I'm only now to the point where I can spec, build, and assess a complete gun that I'd trust my life on....and that's mostly because other people smarter than me have done some of the heavy lifting in knowing how critical parts/components interface and tolerance stack.

Assembling your own AR is awesome, but don't be too quick to have it be a "defense" gun that has a lot riding on it. Much like, would you rather have the first helicopter ride be in something you cobbled together from a kit or something that came from Bell?

I'm pretty sure no one here can honestly say: "Yep, my first AR build went smooth as silk and I totally would do it 100% the same way today."
You make a very fair and valid points. I will definitely keep my expectations realistic. I am also a fan of testing any weapon before trusting my life to it. I have had multiple factory built firearms have malfunctions of one kind or another. I have a 40 cal from a well known brand that when testing with hollow points produced FTFs with two out of three top brands. Granted it is an ammunition related malfunction, I think it proves a point about testing your firearm, and testing with ammunition you intend to use.

I say this to pose the following hypothetical situation:
Say I have two rifles, one factory and one assembled at home. I then test both with 1000 rounds of various ammunition types with various magazine under various conditions etc. Both have zero malfunctions not related to ammunition or magazines.

Is there anything specific that would cause the home assembled rifle more likely to have a failure of some component on round 1001 versus the factory gun?

Non-hypothetically, what part or parts in the above scenario would be most likely to cause a problem? More specifically, excluding quality of parts, what part of the assembly process would be most critical to preventing malfunction? What “QC check” could be done to verify if those critical components were properly interfacing?
 
#6
Hard to say until you get the parts in hand and examine them and then see how things interface with each other. It may be fine; it may not be. Will you know if it isn't?

In the end, I don't have any skin in the game regarding your build. Just offering my $0.02 from someone who has been in your shoes and learned the hard way by making several mistakes in the process despite taking make "safe" choices with components.
 
#7
Please don’t misunderstand me, I was asking because I truly want to know. I wasn’t trying to come off like a smart ass. I appreciate your input and response. I really do appreciate it since I am new to building ARs and I figured there are plenty of folks who know way more than me. I’m just trying to learn as much as I can. I’m sure it won’t be perfect and there will be something that needs tweaking. I’m basically trying to pick your brains so I can learn from your knowledge and experience to do the best build that I can. Thank you for your posts!
 
#8
I'd say check out SOTAR (school of the American Rifle) on you tube and note the tolerance differences in BCG check-up's...and that's just BCG's alone. Also check out some autopsy vids and see some hiccups and screw ups others have made.