AR-15 lower receiver with buffer tube and arm brace installed.
ARBuilds

Assembling an AR Lower – Step 9 of 11: Installing the Buffer Tube and Arm Brace

There are three types of buffer tubes for ARs and the one you pick depends on what you are building.  There is the traditional long A2 fixed stock style buffer tube, the 6 position M4-style telescoping stock tube and lastly the pistol buffer tube. Since I am building a pistol, that will be our focus.  The pistol buffer tube has no provision for a stock and is just a straight tube.  Do not use a rifle tube on a pistol build just to be safe legally.  Other than that, the installation is almost identical other than the backplate (shown below the buffer tube in the next photo) which is indexed for rifles but typically not for pistols.

AR lower receiver parts: buffer tube, spring, castle nut, and arm brace adapter.

Step one:  Install the rear takedown pin assembly.  Insert the pin from the right to left.  Put a dab of Tetra Gun Grease in the detent hole and then push the pin and spring in.  The grease will help retain it.

AR-15 buffer tube, spring, and Tetra Gun Grease for lower assembly
Close-up AR lower receiver with buffer tube and arm brace installed
AR lower receiver buffer tube threads and arm brace attachment point
Close-up of AR lower receiver with installed buffer tube and arm brace attachment.
AR lower receiver with buffer tube installed, part of arm brace assembly.

Step two:  Put the backplate on the tube and thread it into the receiver almost to the end.  Watch the detent spring and make sure it is compressing properly into the hole and not bending.  On pistol builds I will push the plate down with one hand while threading the buffer tube on with the other.  Stop in time to insert the buffer spring and detent in their hole.  Push them down and thread the buffer tube on the rest of the way.  Note, you can stake the tube into position or use a small dab of blue Loc-Tite to hold the buffer tube in position.  Note how the front of the tube overlaps the detent pin just enough to hold it in position.

Installing AR lower buffer tube and arm brace: hand holding buffer tube assembly.
Assembling AR lower: installing buffer tube and arm brace.
Installing AR lower buffer tube and spring during assembly
Installing buffer tube on AR lower receiver during assembly
Close-up of a detent pin being installed into an AR lower receiver.

Step three:  Install the Arm Brace.  The SB Brace I got from Palmetto has a hollow rubber cylindrical hole for the buffer tube to go down.  Of course that thing will not want to slide down the tube by itself.  I lightly lubricate the buffer tube with silicone spray and then slide/hit the brace into place.  Only turn the brace clockwise as you install it lest you unscrew the buffer tube.  I did use a rubber mallet to help get it down the tube faster.

AR lower receiver with buffer tube, arm brace, and WD-40 lubricant
Installing AR lower buffer tube and arm brace assembly
Camp Chef two-burner stove with a large pot, propane tank, and accessories

So with that the brace is installed.  My next post will be about attaching the upper and finishing the assembly.

Sources For AR Parts

The following are all vendors of AR parts including barrels, handguards, triggers, magaziness and what have you that I use and recommend:

Beware no-name knock off websites selling generic import stuff. Some of the parts are counterfeit and not rated for firearms use.

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