Cleaning the Lower Receiver

Clean

Attach the shotgun bore mop onto a pistol cleaning rod or chamber tool handle. Alternatively, you can use a bore brush wrapped in a wipe (wrap enough times to get between 3/4″ and 1″ diameter).
Insert the bore mop fully into the receiver extension. Wipe around the inner diameter of the receiver extension as you pull the bore mop out.

Inspect

Shine a light into the receiver extension and inspect.
Look for any debris remaining in the tube. Repeat step 2, as necessary.
Look for any pitting, cracking, or unusual wear. Replace the receiver extension, as necessary.
Inspect the staking of the castle nut, as applicable. If the staking is not sufficient, re-stake the castle nut per our Castle Nut Staking Tutorial.

Clean

Using a clean and dry wipe, wipe the buffer spring or buffer assembly thoroughly to remove all lubricant and debris.
Using a clean and dry wipe, wipe the buffer, if applicable.

Inspect

Inspect the buffer spring for wear or damage.
- Measure the length of the buffer spring to determine if it has shortened excessively. Replace the buffer spring, as necessary.
  - Carbine: Replace below 10 ⅟₁₆”
  - Rifle: Replace below 11 ¾”
- Inspect the buffer spring for kinks or cracking. Replace the buffer spring, as necessary.
Inspect the buffer for wear and damage.
- Look for gouging on the face of the buffer (where the BCG contacts it). This may occur if there are burrs or rough edges on the back of your bolt carrier. Replace if excessive gouging has occurred.
- Look for gouging on the edge of the buffer face (where the buffer retainer pin contacts it). This may occur if the buffer retainer hole is drilled too far back in the lower receiver, which causes the buffer to crash into the pin before the BCG has returned to battery. If this is the case, there are offset buffer retainer pins that can be purchased.
- Look for excessive scratching, gouging, and any cracking of the buffer body. Replace the buffer, as necessary.
- Make sure the roll pin is still secure in the buffer (where the buffer body meets the bumper). Replace as necessary.
- Inspect the bumper of the buffer for cracking or mushrooming. If the bumper looks beat to hell, is wider than the body of the buffer, or is shattered, you probably have an over-gassed gun. Replace the buffer, as necessary, and address the overgassing.

Clean

Using a nylon brush, brush the trigger assembly, including trigger, hammer, and springs, to loosen any debris.
Using compressed air, blow out any debris.
Using a clean and dry wipe, wipe the hammer.

Inspect

Inspect the hammer and disconnector for unusual wear or damage.

Inspect the striking face of the hammer for gouges, chips, or cracks. Replace the hammer or trigger group, as necessary.
Inspect the hook of the disconnector and hammer for chipping or excessive wear. Replace the disconnector, hammer, or trigger group, as necessary.

Clean

Using a nylon brush, wipes, cotton swabs, scraping tools, and compressed air, clean any debris out of the interior of the lower receiver.
Wipe the out the interior of the lower receiver.
With the pivot and takedown pins in the open position, wipe the shafts of the pins with a clean and dry wipe.

Inspect

Inspect the lower receiver and components for unusual wear or damage.

Inspect the pivot and takedown pins for wear or cracking. Replace the pin(s), as necessary.
Inspect the pin holes for the safety selector, pivot pin, takedown pin, trigger pin, and hammer pin for excessive wear or cracking. If observed, you may need a new lower receiver.
Verify the locking of the pivot and takedown pins in the open and closed positions. If the pins are not secured by the detent, the detent, detent spring, or pin may need to be replaced.
Inspect the bolt catch for excessive wear, chipping, or cracking. Replace the bolt catch, as necessary.
Inspect the bolt catch lugs on the lower receiver for cracking. If present, you may need to replace your lower receiver.
Inspect the magazine catch for excessive wear, chipping, or cracking, especially where the magazine catch latches the magazine. Replace the magazine catch, as necessary.