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AR-15 Lower Receiver Overhaul

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Warning! When handling firearms, always observe safety rules and the precautions set forth in the firearm’s owner’s guide. Be certain that your firearm is unloaded and made safe before proceeding with this DIY.

Brownellslogo4625C Before-4

The AR-15 is one of the most customizable rifles on the market. With multiple alternatives available for virtually every one of its components, its modification possibilities are nearly endless. However you decide to change up your AR-15, knowing how to actually affect these changes will free you up to personalize it to your heart’s content.

Although work on firearms is commonly recommended or required to be done by trained armorers or gunsmiths, these mods on an AR-15 lower receiver are easy do-it-yourself (DIY) projects, as long as you are careful and pay attention to the details. If you are in doubt at any point during this DIY, stop and consult a professional. That being said, if you are up for the challenge and capable of working with your hands, read on and let’s get this overhaul party started.

AR-15 Lower Receiver Overhaul
We’ll tackle the modifications in sections. Parts for each modification will be called out at the beginning of each section.
I. Trigger and Hammer Assembly
II. Grip and Ambidextrous Safety
III. A2 Butt Stock to Collapsible Butt stock & Extended Takedown Pins
IV. Trigger Guard

For this DIY, we sourced the featured parts and specialized tools from Brownells. You can use the part numbers, item descriptions, and prices listed in the spec box at the end of the article to easily find each part or tool on Brownells’ website:

In order to do all of the listed work, you will need the following tools. Having the right tool for the right job makes all the difference.
>Brownells Lower Receiver Vise Block
>Brownells Bench Block
>Brownells CAR-15/M4 Butt Stock Wrench
>Brownells Pivot Pin Installation Tool
>Brownells #3 (3⁄32) Starter Roll Pin Punch
>Brownells #4 (1⁄8) Starter Roll Pin Punch
>Large Flathead Screwdriver
>Curved Pick or Similar Apparatus


We begin with an Aero Precision lower receiver (P/N 953-000-001) with a Double Star Lower Parts Kit (P/N 100-010-669) and DPMS AR-15 A2 Butt Stock Assembly (P/N 231-115-004) already installed.

I. Trigger and Hammer Assembly

Geissele Automatics .154” SSA Trigger


1. With the Lower Receiver Vice Block firmly installed into the vise, place your lower onto the block. Make sure the hammer is not cocked back.

2. Then, use a 3⁄32 pin punch to tap out the hammer pin. The upper, forward pin is the hammer pin. It doesn’t really matter if you go left to right or vice versa. But, be careful not to lose any parts, because the hammer is under spring tension and will jump when the pin is completely punched out. Here, we use a #3 Starter Roll Pin Punch, but since we’re punching out a regular pin, any correct size punch will do.

3. Now do the same with the trigger pin.

4. The lower receiver’s fire control pocket is now clear of the old trigger and hammer.

5. Be sure to read the instruction booklet that came with the trigger kit and follow the manufacturer’s installation steps.

6. Place the trigger into the receiver with its spring legs pointed forward.

7. Install the trigger pin by hammering the pin in, while aligning the pin with the trigger, disconnector, and receiver holes. Geissele triggers come with a slave pin that keeps everything in line making for an easier install.

8. Make sure the hammer spring is oriented with the upper portion of the spring hooked up on the rear of the hammer, while its legs are pointed down.

9. With the legs of the spring pointed back toward the rear of the receiver, force the spring to bend while you place the hammer into position, so that its holes are aligned with the receiver’s holes. The spring’s legs should be pointed back, resting on either sides of the trigger pin you just installed.

10. The spring is going to fight you on this, so it might be easier for you to get the hammer pin started on one end before you hammer in the entire pin in. After it is started, it will be easier to align the hammer with the other receiver hole.

11. Now that the trigger and hammer are installed, it’s time to do a function check. Cock the hammer back. The hammer should lock back and stay in position.

12. Make sure the safety selector works by putting it into Safe position. The trigger should not be able to fire.

13. Now switch it off Safe, and using your thumb, hold the hammer back and pull the trigger.

14. The hammer will release and fall forward, but use your thumb to ease it forward so that it doesn’t slam into the bolt catch or receiver. Gently let it come to a rest.

15. Now with the trigger depressed and held bottomed out in firing position, pull the hammer back until it clicks and locks into place.

16. Slowly release the trigger until you hear and feel a loud click from the disconnector engaging. The hammer should now be in ready to fire position.

17. If all this checks out, you have a properly functioning fire control assembly. If it doesn’t, retrace your steps to figure out where you might have gone astray. Common errors involve the trigger and hammer springs oriented incorrectly. Do not fire the gun if it does not pass this function test.

II. Grip and Ambidextrous Safety

Magpul MOE+ Grip
Battle Arms Ambidextrous
Safety Selector [BAD-ASS]

Grip-Safety-Parts-2 Grip-Safety-Parts-3

1    Remove the grip’s screw through the opening at the bottom of the grip with a screwdriver.

2    A safety detent spring is located at the top right side of the grip. There is also a detent that is located just under the safety selector inside the lower receiver on the same side. Collect those parts and be careful not to lose them when you remove the grip.

3    When the grip, safety detent spring and safety detent are removed and the hammer is cocked back, the safety selector switch will easily come out the other side of the receiver.

4    Now we can reinstall the safety selector. As always, follow the instructions that the manufacturer includes with its product. Here, we are installing a Battle Arms Ambidextrous Safety Selector through the left side of the receiver. Again, the hammer should be cocked back during installation.

5    On the right side of the receiver, we screw in the right side selector arm.

6    After making sure that the safety selector operates correctly in Fire and Safe modes, we reinstall the safety detent, safety detent spring, and our new Magpul MOE+ Grip (in that order).

7    The screw goes in through the bottom just like the standard grip we are replacing.

8    Now that everything is buttoned up, perform another function test, looking for correct operation and feel. If the grip or safety selector doesn’t feel right or operates correctly, retrace your steps and correct any mistakes.

III. A2 Buttstock to Collapsible Buttstock & Extended Takedown Pins

Magpul ACS-L
VLTOR Mil-Spec Receiver Extension
Noveske Rifleworks QD Receiver End Plate
High Standard Extension Lock Nut
Colt H2 Heavy Buffer Assembly
DPMS Carbine Buffer Spring
YHM EZ Pull Pivot & Takedown Pins

Stock-Takedown-Parts-1 Stock-Takedown-Parts-2

1. Depress the buffer retaining pin and remove the buffer and action spring from the lower receiver.


2. Unscrew the screw found at the rear of the butt stock. Be careful, the rear takedown pin detent spring is located where the butt stock and receiver meet on the right side. As the butt stock is unscrewed, it will loosen and the spring will want to jump out. As the stock is slowly removed, grab the spring.

Stock-Takedown-2B Stock-Takedown-2C

3. Following the rear takedown pin detent spring inside the receiver is a detent. Most of the time it’s hiding in there and will need to be coaxed out. Make sure to collect it, so that you don’t lose it, either.


4. Next, unscrew the receiver extension. Again, be careful because another spring will want to escape. Just in front of the open end of the extension are a buffer retainer pin and its spring just underneath it. The receiver extension holds these two parts in place, so unscrewing the tube will sending them flying, never to be seen again. Place a finger or tool on the buffer retainer as you unscrew the receiver extension. Once clear of the retainer, carefully collect the two parts and put them away; you’ll need them during the reinstall.


5. With the butt stock assembly removed, the rear takedown pin can come out. After removing the stock pin, we replaced it with a YHM EZ Pull Takedown Pin.


6. Now let’s prepare the buffer assembly for the collapsible stock for installation. The receiver extension we are installing is a five-position VLTOR Mil-Spec Receiver Extension.

7. Start by screwing the High Standard Extension Lock Nut, also commonly known as a castle nut, on the tube, with the wide notches facing toward the rear.


8. Follow that up with a receiver plate. Here, we are installing a Noveske Rifleworks QD Receiver End Plate. This end plate accepts Quick Detach sling swivels to attach your favorite sling. There’s a protrusion at the 6 o’clock position on the plate that corresponds to a notch in the threads of the buffer tube. Make sure they match up.

9. Reinstall the takedown pin detent and its spring into the receiver.

10. Now screw the buffer tube into the rear of the receiver. When the front of the tube approaches the buffer retainer hole, reinstall the buffer retainer and its spring. Hold them in place until the buffer tube engages the retainer, keeping it from flying out.

11. At the same time, make sure the rear takedown detent pin spring is being pushed in by the rear receiver end plate nice and straight.
12. When all is in position, hand-tighten the castle nut, so that everything is snug.

13. Place the lower back on the lower receiver block. With the CAR-15/M4 Butt Stock Wrench, tighten the castle nut. We tighten it as much as we can by hand without getting all muscleman on it. Many prefer to also stake it in place for extra security.

14. Next, we installed the Magpul ACS-L butt stock, according to its included instruction manual.

15. Now let’s move on to the YHM EZ Pull Pivot Pin. In order to install the pivot pin, the old one needs to be removed. Begin with it pushed out of the receiver.

16. Using a thin yet strong pointed tool, you will need to push the detent that retains it back into the receiver so that you can free the pivot pin for removal. We use an angled pick, which makes things a bit easier, but a sturdy paper clip would do the job, too. Be patient, because the detent spring will want to battle against your efforts, but you will prevail.

17. Now that the old pin is out, let’s put in the new pin. Using the Pivot Pin Installation Tool, slide the detent spring into the tool’s hole.

18. Follow the spring with the detent by pushing it through the tool’s hole with a #3 punch.

19. Carefully turn the tool so that it helps keep the detent and spring retained within the receiver.

20. Now, we can finally install the new pivot pin. With a good solid grasp of the pivot pin, apply a bit of force toward the lower receiver, while sliding it into the receiver front right to left, so that you use the pin to push the tool out. Be careful, because the detent will want to launch out where the pin meets the tool. Avoid this by applying firm rearward pressure, making sure there isn’t a gap between the pin and the tool.

Stock-Takedown-17 Stock-Takedown-18A
21. When it’s in, it should be retained within the receiver, so that it can’t be pulled completely out of the receiver.


IV. Trigger Guard

Magpul MOE Trigger Guard


1. If you’ve spent any time on the gun forums, you will probably have seen the horrifying sight of trigger guard ears that have broken off of a lower receiver, due to a bad trigger-guard install. Let’s not do that. It’s important to brace the ears when uninstalling or installing. Here, we use a Brownells Bench Block to brace that delicate area.

2. With a #4 roll pin punch, carefully hammer out the roll pin. If the roll pin doesn’t want to budge, try heating the area with a torch and try again.

3. The front of a standard trigger guard is kept in by a spring-retained pin. Push it in and pull the trigger guard out.
4. To install the Magpul MOE Trigger Guard, first use the included setscrew to fasten the front of the trigger guard to the receiver.

5. Now, it’s back to the block to brace the receiver’s ears, while knocking the rear roll pin back in. Once the pin is in and flush on both sides, the install is complete.


If you’ve never worked on your AR-15 yourself, you might want to try it out. It’s fun and rewarding, and it can save you a few bucks. Remember to always be careful. When in doubt, double- and triple-check your work before proceeding to the next step. Share your results with us on our Facebook page,; we always like to see before and after pictures of lower receiver overhauls.



080-000-692    BROWNELLS AR-15/M16 LOWER RECEIVER VISE BLOCK    $49.99
080-000-492    BROWNELLS RIFLE BENCH BLOCK    $18.99
080-000-670    BROWNELLS CAR-15/M4 BUTT STOCK WRENCH    $79.99
080-000-244    BROWNELLS #3 (3/32”) ROLL PIN STARTER PUNCH    $6.99
080-000-245    BROWNELLS #4 (1/8”) ROLL PIN STARTER PUNCH    $5.99


100-003-620    GEISSELE AUTOMATICS SSA TRIGGER    $186.00
100-006-786    MAGPUL MOE+ GRIP, BLACK    $22.99
100-009-325    MAGPUL ACS-L CARBINE STOCK, BLACK    $95.99
100-004-756    Noveske Rifleworks QD Receiver End Plate     $24.99
430-000-532    High Standard Extension Lock Nut    $4.99
160-307-200    Colt H2 Heavy Buffer Assembly     $44.99
231-000-261    DPMS Carbine Buffer Spring     $5.29
100-003-690    YHM EZ Pull Pivot & Takedown Pins     $17.99
100-004-156    Magpul MOE Trigger Guard    $8.99

*Brownells’ pricing subject to change

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