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How to Build an AR-15 Upper Receiver

 


How to Build an AR-15 Upper ReceiverToday we are going to look at what it takes to build or assemble an upper receiver for the AR15. This article will be for the first time AR builder. If you are an AR Master Jedi arms builder, this article is probably not for you, but if you want to read it, welcome on board. The way I see this build, we go from the outside inwards, so we will begin with the Ejection Port Cover also known as the Dust Cover. Any Dust Cover will be installed this way, so if you have a personalized or different color, they all install the same.

Let us begin. The number one thing needed for any of this assembly work, but most important for the Ejection Port Cover is slow down and lots of patience.

Ejection Port Cover / Dust Cover

First part to assemble is the Pivot Rod and the E clip. Using  needle nose pliers and the soft face hammer, tap the E clip onto the groove. This part is the “easy to say, kind of hard to do” part.  Likely these parts will end up on the floor, at least the first attempt. Remember to slow down and have patience

When you get that put together, put a drop of oil on the Pivot Rod, not too much, and spread it around with your finger. Place the smooth end through the boss near the barrel or front of the Upper Receiver. OK, now place the Cover in position and the spring in the recessed area, with the long “leg” of the spring towards the front. Hold the short “leg” down with one finger and rotate the long leg under itself to load tension on the spring, place the long leg in the recess to hold the cover open. Now slide the Pivot Rod, through the Cover and the spring, and the final boss.

Now a simple function test will have the Ejection Port Cover hold against the Upper Receiver in the open position, the cover should not flap around or rattle.

Forward AssistForward Assist

Next for our outside moving inwards approach will be to assemble the Forward Assist. One of the special tools needed for this assembly is a Holding Fixture. This tool keeps the vise from marring the surface and keeps the vise jaws from crushing the Receiver.

To begin with place a drop of oil on the pin, and a little dab of grease on the spring. Put the Receiver in the Fixture, and clamp in the vise, not a crushing amount of pressure, just hold it in place. Put the spring over the pin and put the Forward Assist into the hole. Rotate and work the pin to make sure everything moves easily and does not have excessive play.

Next locate and align the holes for the Retaining Roll Pin. Use a 3/32” punch (or similar size) as a slave pin to keep everything lined up, and tap the roll pin into place, pushing out the punch. Just easy taps from the hammer on the roll pin, no need to “drive a nail,” just tap it into place. After all of that is done, check functions, make sure everything pushed easily, and you are done. (image 3) Now, we move to the inner workings.

First part to assemble is the Pivot Rod and the E clip. Using needle nose pliers and the soft face hammer, tap the E clip onto the groove. This part is the “easy to say, kind of hard to do” part. Likely these parts will end up on the floor, at least the first attempt. Remember to slow down and have patience.

When you get that put together, put a drop of oil on the Pivot Rod, not too much, and spread it around with your finger. Place the smooth end through the boss near the barrel or front of the Upper Receiver. OK, now place the Cover in position and the spring in the recessed area, with the long “leg” of the spring towards the front. Hold the short “leg” down with one finger and rotate the long leg under itself to load tension on the spring, place the long leg in the recess to hold the cover open. Now slide the Pivot Rod, through the Cover and the spring, and the final boss. Now a simple function test will have the Ejection Port Cover hold against the Upper Receiver in the open position, the cover should not flap around or rattle.

The Bolt

The Bolt is doing nearly everything when it comes to chambering a round, firing the round and removing the spent cartridge from the chamber. Most suppliers sell the Bolt fully assembled. Meaning that the Bolt has the Extractor, Ejector and Retaining Pins installed. For that reason, and to save some space I am going to follow that lead and not cover the assembly of the Bolt. (image 4)

Ensure the three Compression Rings are lined up correctly. There are gaps in the end of the Rings. These gaps must be offset from one another, so the gasses do not leak past the Rings. Simple to do, just rotate them about 30 degrees from each other. Or one at the 12, 4 and 8 o’clock positions. If the Rings move too easily and wont stay put, apply a dab of grease, (a ridiculously small dab) and that will hold them in place. Do not goop up the Bolt with grease, it will attract and hold the junk that creates malfunctions.

Bolt Carrier

Again, most suppliers will sell the Bolt Carrier with the Keyway (gas port) installed and the Hex Bolts staked. So, I will not cover this assembly again and follow the suppliers lead. (image 5)

The Bolt Carrier needs to be inspected for any burrs left from the manufacturer. Look inside the Bolt Carrier and inspect for grit, or rough surfaces. If anything needs fixed,  200 grit sandpaper can knock that down quickly but may remove the finish. Simple Cold Blue will touch up the area if made from steel. Good maintenance and proper oiling will keep guns from rusting forever.

Firing Pin

Firing Pin protrusion needs to be checked. nearly all firing pins will be right on the money, but this is a critical thing to check on. Too much protrusion will punch out the primer causing some bad things to happen inside the gun. Too little and the primer strike may be too weak to fire the round. (image 6) Checking is easy. Put the Firing Pin in the Bolt, look at how far the pin sticks out of the bolt face. That measurement is supposed to be .030” to be perfect. A Firing Pin Gauge is sold that measures this protrusion with the Gauge and a pair of Calipers. If you do not have this or don’t want to get one, use some feeler gauges to check.

TIP: If your feeler gauges are too big to fit within the bolt face recessed area, blacken the protruding tip of the pin with a Sharpie marker, then remove the pin and measure the blackened area. (Image 7)

Forward AssistBolt Carrier Group

OK, we have checked and ensured all the parts for the Bolt Carrier Group are here and everything is working as it should. Now lets put that together. This may look complicated and foreboding if you have not done it before, but its just a simple assembly of all the stuff you have done up to now. All parts only fit one way, so if it does not fit, it is in the wrong place. See, what did I tell ya? Simple.

Place the Bolt Carrier on the table with the Keyway on top, then place the assembled Bolt inside the Bolt Carrier. Remember the Bolt face with the Locking Lugs or “star” will be outside of the Bolt Carrier. The Bolt should operate smoothly in and out and rotate within the Bolt Carrier. (image 8) Next, we need to install the Cam Pin. The Cam Pin will connect the Bolt to the Bolt Carrier. Put the Cam Pin into the Bolt and align the Cam Pin’s head long side along the Keyway. You will know this is correct when it fits just right. Any other way and it wont work. Easy money.

After the Cam Pin slips into its place in the Bolt, rotate the head 90*, it will now move along the groove and allow the Bolt the rotate. So far, pretty dang easy and all the parts fit and move so it is time to finish off the Bolt Carrier Group. Slide the Firing Pin into the back side of the Bolt, thru the aligned hole in the Cam Pin and protrudes from the Bolt face, again .030”. (image 10) Final step is to put the Firing Pin retainer (cotter pin) in its place on the side of the Bolt Carrier Group. Make sure it fits fully below the Bolt Carrier Group surface that will ride in the Upper Receiver, fitting well inside its recessed area. If this does not fit below the surface area,  the Bolt Carrier Group will hang up, the gun will stop functioning and you will have a massive jamming issue to resolve. If the Retainer sticks out, trim it in VERY small increments until it fits. (image 9) OK, lets put that in the Upper Receiver and make sure it all fits.

Charging Handle

This part will take some more of that patience we used in the beginning. After a few assemblies, this is second nature, but at first, cussing is traditionally used.

Turn the Upper Receiver upside down and place the Charging Handle into its “race” or milled area. The Charging Handle has “ears” on the side and will only fit one way. Look for the relieved areas and put the handle in that spot. Leave it sticking out about two inches of so. Yes, it will be kinda loose and floppy, that is the way it is supposed to be. (image 11) Now, take the Bolt Carrier Group and place it keyway into the Charging Handle groove, again it only fits one way. Now simply push both the Bolt Carrier Group and Charging Handle forward into place. The Charging Handle should lock into place, and release easily when you push on the release. Well Done! You have assembled the “guts” of the Upper Receiver! Now, lets put on the barrel and finish this Upper Receiver Build.

AR15 Barrel and HandguardBarrel and Handguard

Most Barrels are shipped from the supplier with the Barrel Sleeve, Gas Block and Front Sight assembly installed. For this article, we will assume you have ordered your barrel in this fashion. So, that means we just need to assemble the Barrel onto the Upper Receiver. That involves on an old school build, the Delta Ring, Well Spring and Retaining Ring. This will take a few of the specialty tools from the tool list. (Image 12)

Slip the Delta Ring over the Barrel Sleeve and over the Barrel Nut. Make sure the hollow is towards the chamber so the Well Spring and Retaining Ring will fit inside of the Delta Nut recess. Slip the Well Spring into that recess, and then apply the Retaining Ring into the groove on the Barrel Sleeve. Make sure the Retaining Ring is fully seated in the groove and can be rotated easily. This will be critical in a couple minutes.

The new and most popular handguards are the free-floating style. They attach similarly with the barrel nut being designed to hold the handguard. Follow the instructions that come with the handguard if you go this route, and it’s just as easy, maybe even easier than the Delta Ring style. (Image 14)

Now, remove the Bolt Carrier Group and the Charging Handle from the Upper Receiver. Coat the threads of the Barrel Nut and the Upper Receiver with anti-seize. Ensure the Indexing Lug on the top of the Barrel is lined up with the Receiving Groove. The Indexing Lug and Groove ensure the Gas Port is aligned, (more on this in a few minutes). Thread the Barrel Nut onto the threads and screw it down until finger tight. Make sure that everything fits easily and is lined up correctly.

ar15 barrel assemblyPut the Upper Receiver into the Holding Fixture and clamp into the vise. Now, use that Barrel Nut Wrench or the Armorer Wrench on the teeth. The Barrel Wrench or Armorer Tool is custom made for this. There is a ½” hole made for the Torque Wrench. Apply smooth and easy pressure until to 30lbs of torque is reached. Release the pressure, unscrew a bit, and repeat two more times. What we are doing here is making sure the barrel is as square as possible, and the threads are getting the best lock up. Final torque is applied to 45lbs, the armorer books will list this torque at 30 – 80lbs. The reason I say 45lbs will be obvious in the next step or two.

Use a small punch to line up the Gas Tube slots in the Delta Nut, Barrel Nut, Well Spring, and Retaining Ring. If the Barrel Nut needs to be moved, apply more torque until it clears the slot alignment. So, in the end, the Barrel Nut will be torqued to right in the sweet spot of 30-80lbs. The best practice here is to use the Gas Tube Alignment Tool. It is precision made to the exact size of the gas tube. When all this is lined up, insert the Gas Tube. Apply a drop of oil and push the Gas Tube about 5 inches or so into the Upper Receiver. Next pull the Gas Tube forwards and insert it into the Gas Block near the Front Sight. When you push the Gas Tube into the Gas Block, visually inspect that alignment holes line up, double check with that small punch. When all of this is good, install the roll pin.

ar15 gas blockOK, the gas tube is in and all of it is in the right place. The barrel is in, and looking good. Time to get all the goodies working together. Install the Charging Handle and Bolt Carrier Group just like you did before, and visually check that the Gas Tube fits the Keyway on the Bolt Carrier Group. Move the BCG back and forth many times, making sure everything lines up and fits.

OK folks, from here on in, the rest is called furniture and is all about what you like astheticaly and ergonomicaly. Handgrips, compensator choice, sights, or optics, etc. If you are in the market for optics for your build, check out our article on the Best AR15 Scopes.

So, now that you have assembled half the rifle, how hard was that? The Lower Receiver is not that much harder. So, what are we waiting for? Let’s get the rest of that rifle ready to burn up paychecks worth of ammo. See you at the range!

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Loyal Brenzy | huntingmark.com

 

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