NM Rifle Build Part 9

In Part 1, we introduced the series and talked about tools.
In Part 2, we installed the magazine catch and trigger guard.
In Part 3, we installed and adjusted the Jewell Match trigger.
In Part 4, we installed the safety selector, pistol grip and bolt catch.
in Part 5, we installed the pivot pin, recoil buffer components and buttstock.
In Part 6, we installed the forward assist and the ejection port cover.
In Part 7, we installed the delta ring and barrel.
In Part 8, we installed the free float tube and front sight base.

This time, we’re going to install the handguards and flash hider, assemble and install the bolt carrier group, and mate the upper and lower for the first time.

As usual, click pix to make bigger

The handguards are pretty simple. The only difference between the float tube handguards and standard is that the heat shields are removed, and some of the plastic around the front end is trimmed away to make them fit over the float tube. Other than that they are stock handguards and go on the same way that stock handguards do.

Slip the front tabs of the top handguard into the handguard retainer on the front of the float tube.

Pull back on the delta ring.

Try to slip the back of the handguard into the delta ring.

Grunt.

Pull back on the delta ring HARDER, finally get it to pop in.

They actually make a tool for prying the delta ring back but I always thought $29.99 was a bit steep for a piece of bent thin metal rod so I’ve never considered buying one.

Anyway, repeat with the bottom handguard. Make sure they snap together completely after getting the bottom one into the delta ring. Make sure the delta ring is as far forward as it will go, securing the handguards to the float tube.

The last part of the barrel installation is the flash hider.

There are actually two types of washers that can be used for the flash hider. I chose the peel washer. it is basically a washer made up of thin laminated layers of metal. You can peel off layers to make it exactly the thickness you need.

The other style is the “crush” washer. As its name implies, it crushes as you tighten the flash hider which adjusts the thickness dynamically.

I chose the peel washer becaused it seemed to me that the setup would be more consistent and stable for accuracy. Don’t know if that’s right or not, but seemed that way to me.

What we’re trying to accomplish is to get the flash hider torqued to 15 to 20 pound feet with the ports pointing up and the closed side down.

The first time I put it on, with the full peel washer underneath it, when hand-tight, the ports were canted to the right (as we’re looking at it in the picture). To get the ports indexed properly, the flash hider would have to be turned almost another full rotation. No way that’s going to be right.

The best way I found to peel layers off was with a utility knife. The blade was thin enough to get between the layers easily and with good control, but not so thin that I was worried about it breaking.

Find the thickness that you want to peel away and place the blade there.

Then tap it gently with a small hammer to get it started.

Once the layers have started peeling apart, you can just push the blade through to finish it.

After peeling off a layer and trying it, and peeling off a layer and trying it, I finally ended up with getting it about where I wanted it.

As soon as you think it’s in the right ballpark, try torquing it. If you start to go over 20 pound feet, peel another layer and try it again.

20 pound feet really isn’t much torque so it shouldn’t have to turn far to be torqued correctly.

Conveniently, the AR-15 multi tool has a section made for tightening the flash hider.

Also conveniently, it happens to be oriented so it’s easy to tell when the flash hider is indexed correctly…you turn the tool until it is horizontal and the flash hider is oriented properly.

The hole for the torque wrench is in a strange place in relation to the flash hider wrench part, but as long as you keep the torque wrench at a 90 degree angle with the lever point, it will work fine…or at least it did with my torque wrench. By the way, the extension length for this operation was exactly the same as for the barrel nut torquing: 1.5 inches. That means the correction formula was the same. I actually ended up with an indicated torque of 13 to 18 pound feet to get an actual torque of 15 to 20.

The procedure for torquing is the same as for the barrel nut. Torque to the minimum. If the flash hider still isn’t indexed correctly, set the torque wrench to the maximum and continue turning until the max is reached or the flash hider is indexed correctly, whichever comes first. If the max torque is reached first, you need to take it back off, peel another layer from the peel washer and try again.

The next thing on the list is the Bolt Carrier Group.

The BCG consists of the bolt carrier itself which should include the already installed key and screws. If the key isn’t installed, this is a problem because the screws have to be staked. If you don’t have the staking tool, just be sure to order one with the key already installed.

Also included is the bolt assembly. Also should come pre-assembled, but includes the ejector, ejector spring and ejector pin, the extractor, extractor spring and extractor pin, and the bolt rings.

Next you have the charging handle. This is actually not technically a part of the BCG, but is an integral part of the BCG installation so it’s included here. It consists of the handle, the latch, the latch spring and the latch pin.

Finally, the firing pin, the cam pin and the firing pin retaining pin.

The first thing to do is put the bolt into the bolt carrier, and the first step of that is to make sure the gaps in the bolt rings aren’t aligned.

Sort of like piston rings on an engine piston…the gaps need to be staggered.

The bolt orientation in the carrier is critical as well. The ejector is just a round pin in the face of the bolt. The extractor is a wide hook that extends past the edge of the bolt face.

The extractor hooks on the rim of the cartridge as it is pushed into the chamber. The ejector is compressed under the cartridge base.

After firing, as the bolt moves away from the chamber, the extractor pulls the rim of the empty case, and thereby the rest of the case, to the rear and out of the chamber. Meanwhile, the ejector is pushing against the opposite side of the base of the shell casing under spring tension. As the casing clears the chamber and moves into the ejection port, the ejector pushes the shell casing away from the bolt face, out from under the extractor and out of the ejection port.

If the bolt isn’t in the right way, the ejector and extractor are on the wrong sides. that means that the shell casing will try to eject out the wrong side of the receiver…the side that doesn’t have an ejection port for it to pass through. As you can imagine, this doesn’t work very well and you end up with the empty case jammed in the rifle after your first shot. Basically, it turns your fancy AR into a very expensive single shot rifle.

So, insert the back of the bolt into the front of the carrier and push it in as far as it will go, ensuring that the ejector is to the left, and the extractor is to the right. (opposite in this picture because we’re looking at it from the front).

Next is the cam pin.

The cam pin is what rotates the bolt in the carrier to lock it in the breech when the bolt is closed, and to unlock it so it will open after firing.

There is a large hole that passes through the bolt from top to bottom.

Line that hole up with the elongated hole in the top of the bolt carrier.

Rotate the cam pin so that the hole in it is crosswise to the bolt carrier.

Then insert it into the bolt carrier and bolt through the elongated hole in the carrier.

If you have the cam pin turned the wrong way, it simply won’t go in because the bolt carrier key will be in the way.

Once the cam pin is fully inserted into the bolt and bolt carrier, turn it a quarter turn (either direction…it doesn’t matter).

Now, with the hourglass shaped part to the rear and the pointy end toward the front of the bolt carrier, insert the firing pin through the bolt carrier and bolt from the back.

With the firing pin as far forward as it will go, insert the firing pin retaining pin through the recessed hole in the left side of the bolt carrier and seat it fully.

The “eye” of the firing pin retaining pin should fit down into the recess in the bolt carrier.

OK, now the BCG is together.

The next step is to put the charging handle into the receiver. The charging handle travels along a channel in the top of the receiver. The channel in the receiver has cutouts that the rails in the charging handle will slip through.

The hollow side of the charging handle should be pointing down…it’s up in this picture because the receiver and charging handle are upside down to make them easier to see.

Basically, put the charging handle in the receiver and, while pressing it against the top of the receiver, slowly start pushing it in. When you reach the right spot, the charging handle will slip through the gaps and pop up into the channel it rides in.

Next, make sure the bolt is fully extended from the bolt carrier. The cam pin should be directly under the bolt carrier key and if you pull on the bolt while holding the bolt carrier, it shouldn’t come out any farther.

Now, with bolt face toward the front of the reciever, pull the charging handle out just enough that the bolt carrier key will slip up into the hollow bottom of the charging handle.

Then push the bolt carrier and the charging handle the rest of the way into the receiver together.

If the ejection port cover is closed, it will pop open as the bolt carrier passes it.

When fully inserted, the bolt will rotate and lock into the breech and the charging handle latch willl lock the charging handle into the receiver.

The next step is to mate the upper and lower receivers together for the first time.

One of the idiosyncrasies of the AR platform is that the upper and lower receivers generally don’t fit together tightly. This isn’t normally considered a problem because it doesn’t affect the bore axis/sight plane relationship, and therefore shouldn’t affect accuracy in any significant way.

The movement created by this loose fit can, however, be distracting…which can affect accuracy…and competition shooters usually try to eliminate it. There are several methods at varying expense levels and effectiveness to reduce or eliminate the slop:

Some manufacturers make matched “national match” upper and lower sets that are specifically made to fit tightly together. Another method is to “glass bed” the action where the gap between the receivers is filled with fiberglass reinforced resin. Another common method is special tightening pivot and takedown pins that are deigned to clamp the receivers together and eliiminate the slack. Or you can go the cheap and easy route like I did and just use an accuwedge.

An accuwedge is a rubbery synthetic insert that fits in the lower receiver below and behind the takedown pin.

As the receiver closes, the accuwedge “wedges” itself into the gap.

The upper and lower receivers are connected at two points. First line up the pivot pin holes at the front of the two receivers…

…and press the pivot pin into place. Sometimes this takes some jiggling to get it all lined up. You should feel the detent “snap” the pivot pin in place as it seats fully into the receiver.

With the pivot pin locked in place and the accuwedge positioned at the rear of the lower reciever, close the two receivers together and press tightly to overcome the tension created by the accuwedge.

And then press the takedown pin in to lock it into place just like you did the pivot pin.

And there you have it.

The only things left are the front sight post and rear sight installations.

Click here for part 10

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