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Notes on the assembly of the AR pattern rifle

1616 Views 12 Replies 7 Participants Last post by  Ramone
Readily available parts of all sorts make the AR pattern Rifle a Do-It-Yourself-ers Dream.

It is not at all difficult to assemble- any idiot can do it- and the intra-webz is full of examples of this fact.

things to make sure that you order for a full build

Lower Receiver: This is the only 'controlled' part- by Law, the Lower Receiver *is* the Rifle, and so, it must be purchased through an FFL, with a NCIC. The Quality of most available Lowers is outstanding- while there are always a few bad ones that slip through, the majority of 'Off the Shelf' (OTS) units are are of excellent quality. The primary variance seen between various suppliers seems to be the finish .

Lower Parts Kit: These are ALMOST as good as the Lower, quality control wise. Shop price, But look for a more established Supplier. The LPK includes a trigger guard, Fire Control Parts (Trigger/Hammer/Selector + springs and Pins) Pivot/take-down pins (and springs) Mag Catch, and Bolt Catch (both with pins and springs), Buffer retaining pin and spring, and usually a Pistol grip and Pistol grip Mounting screw.

To complete a lower assembly, you will need a Receiver Extension (aka Buffer Tube) Buffer, and Buffer Spring, and a Buttstock. Telescoping M4 type Buttstocks require a Castle Nut (usually included). Receiver Extensions come in either 'Mil-Spec' or 'Commercial' sizes, there being a slight Difference in O.D.. Springs and Buffers will fit either, But if you are not buying a complete assembly, do make sure that the stock and the Receiver Extension match.

To assemble these parts into a complete lower, you will need a pair of Water Pump Pliers (aka 'Channel Locks'), Masking tape, a tiny 'eyeglass' type screw driver, and a medium sized or larger plastic bag. A set of allen keys will serve as alignment tools.

A mounting block (The ones I've seen are basically Dummy Magazines that can be clamped in a vise) really seems unnecessary to me- ditto for hammers and punches. A Special Pivot pin assembly tool is nice, but I have always done fine with a tiny screw-driver. Instead of trying to drive pins in with a hammer, I find using a pair of WP Pliers as a hand press to work just fine, and it won't break or mar anything ( cover the jaws with Masking Tape). For a M4 type stock, you WILL need a hammer and Punch to 'Stake' The Castle nut

Most of the assembly should be done inside of the plastic Bag- especially when dealing with the teeny-tiny Pivot pin detents and springs.

Upper Receivers come in 3 basic varieties- M16 (no fwd assist or brass deflector, with Carry Handle) A2 (FA & Brass Deflector with a Carry Handle) and A4 (FA & Deflector, with 'Flat top' Rail). Some (most?) will have 'M4 type' feed ramps, which should be matched with a barrel that has them as well. Standard Feed ramp Upper with a M4 Feed ramp Barrel is OK, But M4 feed ramp Upper with standard ramp Barrel is not OK.

A complete Upper Receiver has a Bolt Carrier Group, a Charging Handle, A Dust Cover (with pin, Spring, and C clip) and a Forward Assist (with Spring and Pin). A 'Stripped' Upper is just the Upper Forging.

For a Complete Upper Assembly, you will Need a Barrel (almost always sold assembled with a 'Barrel Extension'- the part that the bolt engages), a Gas tube, a Gasblock (or Gas Block/Front Sight Assembly aka FSA) a Gas Tube Pin, a Barrel Nut, and a handguard Assembly- for the Standard type, you will need a Delta Ring, Spring, and snap ring, and a Handguard Cap. A 'Free Floating' Handguard will often require (and is usually sold with) a specialized Barrel Nut, or some other specific hardware.

You may need a Muzzle Brake, depending on your Barrel Choice. Gas Blocks or FSAs require either Pins or Set Screws. Handguards and Gas tubes should be matched to Barrel Gas System Length (Carbine, Middle, or Rifle). Assembling the barrel to the upper (and an M4 type Buttstock) is easier with a 'Armorers Tool' but you can usually get it done without one.

If you don't have 'Calibrated Hands', you'll want a torque wrench, or a friend with calibrated hands.

I always take all the parts, Slather them with CLP, and let them sit like that for a day or so, sometimes even heating and cooling them (MILDLY! like front the freezer to direct sunlight for a few hours) to let the CLP fill the pores, then wipe them dry before assembly. This is sometimes called 'oil buffing'.

Chrome BCGs are wonderful things, IMX. WAY easier to clean and clean well than standard coatings.

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The Above DOES NOT cover issues of legality of Stocks, Muzzle Devices, etc, in light of the NYS AWB.

TO THE BEST OF MY KNOWLEDGE, you CAN legally order/own an M4 Style Stock and assemble it, as long as you make it permently NON Adjustable upon assembly.

Likewise, while a Muzzle Device Must be pinned & welded, you can have that done in NY, after ordering the parts.


I am not a gunsmith, nor an armorer, either. Any one that wants to add to or correct anything above is welcome to.
My first build was done sitting in front of the computer watching the videos from Brownells web site. Very easy to understand.

Nice write up. I would like to add something about the different uppers. The Term "M16" is a bit confusing since it has been used for several uppers.

601/604/SP1 uppers - No forward assist or shell deflector. A1 sights and carry handle.
M16A1 (603) - Tear drop forward assist, no shell deflector, A1 Sights and carry handle
605 (very rare) - Forward assist milled off leaving hump, No shell deflector, A1 sights and carry handle.
C7 (Canadian) - Tear drop forward assist, has shell deflector, A1 rear sights.
M16A2 - Has A2 sights that are adjustable for elevation. Round forward assist and shell deflector.
M4 - Flat top with M4 cuts for M4 carbine. Round forward assist and shell deflector.
M16 A3 and A4 - Flat top without M4 cuts for rifles. Round forward assist and shell deflector.

That covers most of the upper receivers used to build most AR15 rifles produced. I included some model numbers but most uppers were used in many different variations. If anyone is interested in photos of different receivers let me know and I will take some.
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Important to note, that once you leave the .223/5.56 AR15/M16 arena with AR's there is really no Military Specification with the exception of the M110. So many Manufacturers parts are not interchangeable with others. More planning is necessary when building a .308 to be sure parts will fit and work properly together from different manufacturers.

Sorry if this question sounds dumb (or is known by everyone but me), but as a LI-NY resident this has always confused me. Any guidance would be greatly appreciated.

I always wanted to build my own, but was never quite sure what is/was legal as far as the AWB goes.

Can I order any lower receiver as long as it doesn't actually say "AR" on it? Is something from PSA or DPMS fine?

Do almost all .223/5.56 lowers go with almost all uppers? (Can you put a PSA upper receiver onto a CMMG lower?)

What about the upper receiver, does the barrel have to be at least a certain length? Every kit I see, the barrels always seem to be 16" and I thought the law was 18.5"

If there's a better place to go for these answers, I'd love to be pointed in the right direction. I would love to know what I can/can't order and maybe get lucky with some holiday sales.
ADIDAS247 I can help you with some of your questions.

The lower receiver can not say AR15 on it if made after September 1994. Not an issue since no one other than Colt stamps them that way. And even Colt offers models that do not include the AR15 marking. So lowers are easy to find.

Yes, 223/5.56 quality lowers and uppers will work together. Some fit tighter than others but this isn't an issue.

Barrel must have a total length of 16" or more. 18.5 is for shotguns.
AR_Guy said:
ADIDAS247 I can help you with some of your questions.

The lower receiver can not say AR15 on it if made after September 1994. Not an issue since no one other than Colt stamps them that way. And even Colt offers models that do not include the AR15 marking. So lowers are easy to find.

Yes, 223/5.56 quality lowers and uppers will work together. Some fit tighter than others but this isn't an issue.

Barrel must have a total length of 16" or more. 18.5 is for shotguns.
Oh, well in that case I think I am going to buy myself an early Christmas present. I thought I would have to look for very specific items.

Thanks AR_Guy. Now I'm off to find the best possible deal.
This DVD is well worth the investment if you are new to the idea of building your own AR....
The Oct 14 review is mine.
Thanks to all- especially AR_Guy, for the additions, and Excellent review, Walker!

I mostly wanted a rundown of parts needed, which was what I found toughest in my first builds- it's kinda frustrating to be ready to start, and then discover that one piddily part is missing.
Nice write-up Ramone... Well done.

TTSkipper said:
Brownells has great videos for assempbly and a checklist for ordering parts on their website.
Oh sure- Now you tell me! ;)
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