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AR-15 Lower Receiver From A Stripped Receiver And Lower Receiver Parts Kit

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The guide below will help you put together your AR-15 lower receiver from a lower receiver parts kits and a stripped receiver. If you have any questions or valuable tips to share with the 80-lower gun community hit us up on Facebook!

TOOLS

Now if you are ready to get started check out some of the tools we’ve listed below and consider using them. While none of them are necessary, they sure make it easier to put together the lower receiver parts kit.

At a minimum, grab a hammer to drive in the roll pin punches and use the very convenient roll pin holders to start the roll pins. When driving the roll pins, grab a block of wood and use the base to support the receiver when driving the roll pins.

Another handy tool for building a few lowers is a #10 flat-blade screwdriver which can be used for A2 stock screw and some pistol grip screws but you can also use an Allen Key for the pistol grips.

Another handy tool to consider grabbing before you get started is a telescoping stock wrench to tighten the telescoping stock lock ring.

The last tool you should grab is a pivot pin installation tool which comes in handy for building lowers in general.

 

ASSEMBLY

As you start the assembly follow the steps presented below for success!

Parts needed:

  • A magazine catch
  • A magazine catch spring (this is the largest spring in the kit)
  • A magazine button (some are plastic, some metal)

Tools needed:

  • 5/32" roll pin punch

Tip: Take special care when turning the magazine catch to avoid rubbing against the hump around the bolt catch. It is possible to scratch the receiver.

ASSEMBLY OF THE MAGAZINE CATCH

  1. Attach the magazine catch with the recess on the left side of the receiver.
  2. Install the spring onto the threaded portion of the magazine catch from the right side of the receiver.
  3. Screw (3 or 4 turns) the button onto the threaded portion of the magazine catch.
  4. Use a punch (larger than hole in magazine button) to push in the magazine button so you can turn the magazine catch (clockwise) until the end of the catch is flush with the magazine button head. Then hold the receiver and press the punch against the table to prevent the bolt catch from getting in the way. Then as you turn the magazine catch into place put something between the punch and the magazine catch button to prevent marking it.

Ask Yourself: Does depressing the magazine release button push the magazine catch out of the magazine well into the lower receiver?

Ask Yourself: Does the spring return the magazine catch to engage in the magazine?

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Parts needed:

  • A trigger guard assembly (metal or plastic with detent installed on the front end)
  • A trigger guard roll pin (larger of the two roll pins)

Tools needed:

  • A hammer
  • 1/8" roll pin punch

Tip: Make sure that the small block of wood is supporting the bottom flange and that the trigger guard is in position supporting the top flange otherwise you risk bending or breaking off one of the flanges.

Tip: Also watch as you put in the roll pin that it is going through the hole in the trigger guard correctly.

ASSEMBLY OF THE TRIGGER GUARD

  1. Start by attaching the front of the trigger guard assembly to the receiver using the detent.
  2. Now lay the receiver on the block of wood to drive the roll pin into the receiver and rear of the trigger guard using the drive pin punch.

 

Ask Yourself: When you depress the detent on the trigger guard are you able to pivot the trigger guard open?

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Parts needed:

  • A bolt catch
  • A bolt catch buffer
  • A bolt catch spring (easily confused with the disconnector spring; disconnector spring is tapered though)
  • A bolt catch roll pin (smaller of the two roll pins)

Tools needed:

  • 3/32" roll pin punch
  • 5/32" (or larger) punch

Tip: Take special care to make sure the pin is in place before driving it. Also ensure that it is held securely in place when striking the punch. To help avoid scratching place fiberglass packing tape (2 layers thick) or cloth over the receiver just between the receiver and the punch.

Tip: It can be very difficult to get this pin started; you might want to try squeezing the roll pin on one end with pliers or the vise before starting. If you don't have a roll pin holder, try holding it in place with a pair of needle nose pliers while you drive using a 5/32" punch.

ASSEMBLY OF THE BOLT CATCH 

  1. When installing the bolt catch, first drive the roll pin halfway into the rear hump from the rear of the receiver using the roll pin holder.
  2. Install spring in hole on left side of receiver.
  3. Install bolt catch plunger on top of spring with round portion on top and small end into receiver. Make sure it moves freely in its hole.
  4. Install bolt catch in receiver; it only fits on one way.
  5. Use a 3/32" punch to hold the assembly by placing it through the front hump.
  6. The pin can be driven the rest of the way from the rear as the punch will be pushed out and while holding the bolt catch in correct alignment.

Ask Yourself: Under tension from the spring does the bolt catch function smoothly?

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Parts needed:

  • A pivot pin (larger of the two large pins)
  • A pivot pin detent (same as takedown detent; both sides usually rounded)
  • A pivot pin detent spring (same as the takedown detent spring, so there are two in a kit)

Tools needed:

  • A pivot pin installation tool
  • 3/32" drive pin punch

Tip: This is perhaps the hardest part of the lower assembly, so if available, install the installation tool. If you do not have an installation tool, it can be difficult to get the pivot pin inserted without losing the detent and/or detent spring; if these parts do fly out, they can be very hard to find. The idea is to insert the spring and detent, and then compress them as you insert the pivot pin. A pair of needle-nose pliers can be helpful. It is difficult to remove the pivot pin once installed, so make sure you do it right the first time and make sure you've cleaned out the detent/spring hole with a drill bit before inserting the spring.

ASSEMBLY OF THE PIVOT PIN

  1. Insert the spring and the detent into the receiver.
  2. Compress the detent into the recess using a 3/32" punch and rotate the tool.
  3. Push out tool with the pivot pin and rotate it until the detent is in the groove of the pivot pin.

Ask Yourself: Does the pivot pin detent prevent the pivot pin from coming off the receiver?

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Parts needed:

  • A trigger
  • A trigger pin
  • A trigger spring
  • A disconnector
  • A disconnector spring

Tools needed:

  • 5/32" drive pin punch

ASSEMBLY OF THE TRIGGER

  1. Should the trigger spring onto trigger with ends of spring forward and under.
  2. Install the disconnector spring with the wider portion of spring down towards the trigger and push it until it locks in.
  3. Position the disconnector on top of the trigger, where the trigger pin will hold both into place.
  4. Insert the trigger assembly into the receiver.
  5. Insert the trigger retaining pin through the receiver, trigger, and disconnector. The trigger pin has 2 grooves in it; one in the middle of the pin and one off to one side. Insert from the left to the right, with the groove to the left.
  6. Insert the hammer pin from the opposite side to help align things as you push the trigger pin in and the hammer pin out. Next, push down on the trigger assembly to align the holes and get the pin in all the way.

Ask Yourself: Does the trigger pivot smoothly when depressed?

Ask Yourself: Does the disconnector pivot when pushed?

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Parts needed:

  • A hammer (with J-pin installed)
  • A hammer spring (larger of the two similar springs)
  • A hammer retaining pin

Tools needed:

  • 5/32" drive pin punch

ASSEMBLY OF THE HAMMER

  1. Install the spring onto the hammer (ends of spring to rear and shoulder on back of the hammer)
  2. Install hammer in the receiver with feet pointing rearward away from hammer.
  3. Use 5/32" punch to retain hammer in place as you insert the hammer retaining pin.
  4. Like the trigger pin, you may have to push down and align the holes perfectly in order to push the pin in all the way.
  5. Ends of the hammer spring will rest on top of the trigger pin, with one end in the groove on the trigger pin.
  6. Inserting the hammer pin may require some effort, as the J-pin in the hammer will catch the grooves in the pin.

Ask Yourself: Does the hammer lock to the rear when pushed back?

Ask Yourself: Does the hammer pivot forward when the trigger is pressed?

Ask Yourself: When releasing the trigger, push the hammer back – does it lock and get caught by the disconnector?

Ask Yourself: Does releasing the trigger cause the hammer to pivot fully forward? It should NOT.

Ask Yourself: Does the hammer fall when the trigger is pressed?

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Parts needed:

  • A safety selector

ASSEMBLY OF THE SELECTOR

  1. With the hammer cocked back, insert from left side of receiver, selector pointing up in the 'fire' position.

Ask Yourself: Does the selector rotate freely?

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Parts needed:

  • A selector detent (one end is flat, the other pointed)
  • A selector detent spring
  • A pistol grip
  • A pistol grip screw (Allen-head or slotted pan-head screw)
  • A lock washer

Tools needed:

  • Allen key//flat-blade screwdriver (depending on screw type)

Tip: The selector cannot be rotated to 'safe' unless the hammer is cocked.

ASSEMBLY OF THE PISTOL GRIP

  1. Install the detent (pointed end towards the selector) and the spring into the receiver from the bottom.
  2. Compress the spring with the grip and make sure the spring fits into the hole in the grip.
  3. Check the function of the selector with the grip held in place; if it is unable to rotate you may need to either cut the spring, or clean out the hole in the grip.
  4. Secure the grip in place with the screw and the lock washer.

Ask Yourself: Is the selector able to move from safe to fire and click in place? It should not move past the ‘safe’ or ‘fire’ positions.

Ask Yourself: With the selector on ‘safe’, does the cocked hammer release when the trigger is pressed? It should NOT.

Ask Yourself: With the selector on ‘semi’, does the hammer release when the trigger is pressed?

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Parts needed:

  • A takedown pin (smaller of the two large pins)
  • A takedown pin spring
  • A takedown pin detent
  • A stock
  • A buffer extension
  • A retainer
  • A retainer spring
  • A buffer
  • A buffer spring

Tools needed:

  • #10 (or larger) flat-blade screwdriver

A2 STOCK

  1. Insert the retainer spring and the retainer into the recess in the lower.
  2. Install the buffer extension tube and press the detent when necessary. Next torque to 35-39 ft - lbs to add a spacer onto the stock tube and insert the stock.
  3. Install the takedown pin with the groove to the rear and install the detent and the spring from the rear of the receiver.
  4. Compress the spring with the stock and secure the stock in place with the self-locking screw.
  5. Insert the stock screw from the rear into the stock.
  6. With the hammer down, insert the buffer spring and the buffer into the buffer tube until the retainer snaps up to lock it in place.

Ask Yourself: Does the takedown pin and buffer retainer function?

[[IMAGE]]

Parts needed:

  • A takedown pin
  • A takedown pin spring
  • A takedown pin detent
  • A telescoping stock
  • A buffer extension
  • A backplate
  • A locking ring
  • A retainer
  • A retainer spring
  • A buffer spring
  • A buffer

Tools needed:

  • Telescoping stock wrench

TELESCOPING STOCK

  1. Insert the retainer spring and the retainer into the recess in the lower.
  2. Install the buffer tube, the backplate, and the locking ring onto the receiver and depress the retainer when necessary to get it to rest under the extension tube. (Turn tube until it is about 1/4 turn past the correct location)
  3. Install the takedown pin with a groove to the rear and install the detent and spring from the rear of the receiver.
  4. The backplate will now hold the spring in place when you turn the extension tube back 1/4 turn.
  5. Tighten the locking ring using the telescoping stock wrench.
  6. Insert the buffer spring and buffer (with the hammer down) into the buffer tube until the retainer snaps up to lock it in place.

Ask Yourself: Does the takedown pin, stock, and buffer retainer function properly?


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