Assembly of AR15 upper - step by step

[moog5050]

Following up on Chefs build, I figured I would offer a step by step post of how to assemble an upper.   
 

step 1.  Pin gas tube to gas block.  I forgot to take pictures of this as I went but it’s the most tedious part of assembly.  First you need to ensure that your gas tube is the correct length based on barrel length (carbine, rifle or rifle plus 2”).  The 22 nosler I am putting together required a plus 2 gas tube as per barrel specs.  Often the tube comes with the barrel but not always.  First photo shows rifle and plus 2 tubes by comparison.   The tube comes with a roll pin.  Don’t lose it!
 

Second photo shows installed pin.  To install pin you really need roll pin punches.  They have a hole in the tip to help hold the pin.  I use a bigger one just to get the pin started in the block.  Then a smaller one that has a slight indentation that is just big enough to cover the pin.  Line it up and drive it through with a hammer.   The pin will want to flare out and a few hard whacks is better than trying to tap it home to prevent flaring.  The pin punch helps in that regard too. Drive it until it’s level with the edge of the block.  Having some type of block to stop the block from rolling when driving it home helps a ton. 
 

last photo shows the starter and finishing punches I used.  

[moog5050]

Step 2 - assemble the upper by hand to ensure everything fits.  Properly.   
 

1. slide barrel in upper receiver.  The barrel extension has a pin that fits in notch on receiver so no worrying about indexing.  

2. hand tighten barrel nut

3.  Loosen set screws on block

4. Install block with gas tube through port - note dimple in barrel for block set screw   

5 slide handguard over   
 

Everything should be free floating.   Handguard tightens against barrel nut    But the guard should not touch the tube, block or barrel   

 

[moog5050]

Now I will note that handguards all come with their own barrel nut.  But not all barrel nuts use the same tool to tighten to torque specs.   So make sure you take note of what tool is required to tighten barrel nut. This nut requires a 1 1/4 crows foot that attaches to a 1/2 drive on a torque wrench.  Not found at your local store.   And some manufacturers have a proprietary wrench that you must buy like white oak armament.  Add $40 to cost. 

[moog5050]

Step 3 

Now you know everything fits so disassemble it

[moog5050]

Step 4 - not required but if you want to do everything possible for best accuracy next is lapping receiver.   
 

requires a lapping tool from brownells.  
 

install receiver in vise (with wood to not mark receiver and not too much force)

add some lubrication to lapping tool and install in drill.   
 

next add some lapping compound to face of receiver where barrel extension inserts.  
 

spin drill slowly checking frequently as to whether finished is removed.  If some finish is removed before the rest you know it wasn’t perfectly square.   Lapp just enough to remove all finish.    
 

photo 3 is lapping tool and receiver

photos 2 and 1 are an example of before and after.  

[moog5050]

Ok your receiver is now perfectly squared up.   Clean everything with alcohol.  You want to be sure the receiver where the barrel extension inserts and the barrel extension are perfectly clean for reasons I will explain next.  

[moog5050]

Now comes the fun part, assembly.   
 

I prefer a reaction rod for holding the receiver and barrel in a vice vs a receiver block.  Reason being is that the rod inserts into the lugs in the barrel.  Far stronger that torquing the aluminum receiver in a block.  
 

This is a reaction rod inserted in the vice.   Slide receiver over it.
 

 

[moog5050]

All lugs on AR15 barrels are the same size so as long as you are building an AR15, the same reaction rod should work.  

[moog5050]

Step 6 - installing barrel.   
 

there is lots of debate over whether bedding the barrel extension into the receiver is needed.   They fit tight to begin with and then the barrel nut is torqued to 30-80ft lbs so many think it makes no difference.  
 

that said, some well know builders of precision rifles swear by it.   It’s a very simply process of smearing bedding compound on the extension before inserting it.  Obviously you don’t want the compound in the barrel but just on the extension to fill any gaps between the extension and receiver. 
 

most use some type of loctite as a compound.   Loctite 620 and 609 is often recommended but being a wimp that wasn’t sure I want the receiver too permanently attached to the barrel I decided I would try blue loctite as many do and swear by it.  Easily removed if needed. 
 

 Coat the barrel extension with the loctite and slide it into the receiver and then clean any that is pushed out well. 

[moog5050]

Next you need to grease the receiver threads to prevent galling.  This is the grease often recommended. Apply grease liberally.  

[moog5050]

Step - lost count.  
 

Now we need to torque the barrel nut.   I find it strange that the torque range is 30-80ft lbs but so be it.  Pretty wide range.   Note that some barrel nuts must be index to ensure that the gas tube free floats.  They have a milled out channel.  And some hand guards require the barrel nut to be indexed so that the guard is square to the receiver.   My nut required neither but keep that in mind as you may need to use that range to index the nut properly. 
 

Anyways, start by torquing to 30lbs, then back it off, next torque to 40lbs and back off.  This stretches threads a bit to ensure final torque will be accurate.  Now the next time is where I wanted my final torque and if you needed to index, now is the time to pay attention.  
 

I wanted final torque at 50lbs.   That’s my homemade crows foot since I could not find one locally.  I drilled a 1/2 “ hole in the wrench and squared it off with a file. Voila. 

Edited March 7, 2020 by moog5050

[moog5050]

Now that the barrel is torqued, wipe off any grease and install the gas block and tube.  Remember that dimple in the barrel as it lines things up nicely.  The block will sit against a shoulder that is cut into the barrel. 
 

 Check to ensure tube is not pressing against nut and is free floated into receiver.  Add some blue loctite to gas block set screws.  

[moog5050]

I forgot to mention, when pinning gas tube, the bend in the gas tube always goes up!

[moog5050]

Time to install your hand guard.  Most are a pinch fit over the barrel nut.   Slide it on, line up the rail and tighten it down to specs. Don’t forget blue loctite on screws. 

Edited March 7, 2020 by moog5050

[moog5050]

That’s it.  Clean that new barrel well.  Slide in your bolt carrier group and charging handle and attach to your lower.  
 

Go and shoot!

[NonTypical]

Out of likes. Thanks for posting. 

[moog5050]

10 minutes ago, NonTypical said:

Out of likes. Thanks for posting. 

No problem.   It’s a piece of cake.  I can see it being quite addicting to build uppers and swap barrels for new calibers.  Fun of the modern sporting rifle.  Lol

[NonTypical]

9 minutes ago, moog5050 said:

No problem.   It’s a piece of cake.  I can see it being quite addicting to build uppers and swap barrels for new calibers.  Fun of the modern sporting rifle.  Lol

I’ve had the desire to get into it for some time now. I’ve been wanting to do a full build, but with so many choices it can be a bit overwhelming. That’s why I figured that maybe I’d just buy one to start with and experiment from there. 

[moog5050]

3 minutes ago, NonTypical said:

I’ve had the desire to get into it for some time now. I’ve been wanting to do a full build, but with so many choices it can be a bit overwhelming. That’s why I figured that maybe I’d just buy one to start with and experiment from there. 

Take you time and build what you want.   It’s not very difficult and it’s fun.  The only thing you need to buy through an FFL is the stripper lower receiver.  Everything is shipped to your door.  And the lower is just as easy as the upper to assemble.  Couple of springs and detents but once you know where they go under stock and pistol grip, it’s really simple.  

[moog5050]

Forgot to mention, when you buy the bcg, take it apart, clean and lube.  Lots of videos on it.  I also lube the channel in the upper where the bcg rides before sliding it in.  

[Gencountyzeek]

Well written moog.

[moog5050]

6 minutes ago, Gencountyzeek said:

Well written moog.

Takes more time to write it up then do it as you know.  Lol

[Gencountyzeek]

Great lookin barrel btw, criterion?

[moog5050]

5 minutes ago, Gencountyzeek said:

Great lookin barrel btw, criterion?

Rainier ultra match.  It does look high quality.  Haven’t shot it yet but reviews are great.  Semi reasonable cost with a 10% discount code I got just by asking.  
 

and they have a no questions asked return policy if it doesn’t shoot to your satisfaction.  I think 90 days. 

Edited March 7, 2020 by moog5050

[moog5050]

Something I should have mentioned in post 1.   In addition to confirming the required length of gas tube per barrel specs and whether it’s included with barrel purchase, you also need to confirm that the inner diameter of the gas block matches the outside diameter of barrel where gas block mounts.   Like the tube, the gas block may be included with the barrel (white oak does) but most don’t.  But all barrels and gas blocks advertise the ID and OD measurements.     
 

You can also consider an adjustable gas block that can allow for different gas pressure but it’s really only needed if tuning a light weight bolt carrier group which theoretically reduces felt recoil.   Honestly for a 22 cal build recoil is not a consideration for me and a standard gas block is just fine.  

and when ordering a hand guard, be sure the ID of the guard is bigger than the OD of the gas block if the guard is long enough to cover the block.   You will realize quick when mocking up the assembly if you messed up here.  Don’t ask how I know.