If the bolt assembly is not cleaned properly, carbon deposits will build up to such an extent that the hammer will not fully enter the trigger, or the bolt itself may not fully enter the battery, causing retrieval problems. The best way to start cleaning the bolt carrier is to apply a small coat of CLP or other gun cleaning solvent to each of the BCG parts. After cleaning small areas of BCG, be sure to clean every part including the hammer, locking pin and cam pin to remove any carbon deposits. Using a Rand Bore and Bolt Cleaner (B&BC), clean the inner surfaces of the upper with a nylon brush.
When cleaning other parts, stop every few minutes to pass a few more solvent-soaked patches through the hole. Lubricate the tabs of the bolts and you will see a color change everywhere (heavy metal mark on contact with metal).
Be sure to use thinner and a wire brush on the front of the bolts, as cooking can build up brass and carbon deposits. When cleaning the bolts, any solidified carbon deposits on the tail of the bolts must be removed. It may be necessary to wet a portion of the bolt and wire brush thoroughly to remove carbon deposits. The bolts may need to be dipped in solvent and this plaque will need to be removed with a wire brush.
There will also be carbon build-up at the base of the bolt hole in the bolt, so use a carbon scraper to clean this part to thoroughly scrub the deposits.
Clean the inside of the bolt holder wrench with an AR-15 gas pipe cleaner soaked in a cleaner / degreaser such as External Crud Cutter Cleaner / Degreaser (# 6-1210383, $ 9.41). Use a cleaning pad or brush with cleaning solution to remove dirt or carbon deposits from the holder. Then clean the center channel if the hammer is a valve head and the gas wrench with a pipe brush or cotton swab. Moisten the inside of the bolt with solvent and use a cotton swab to remove debris.
Use one or two Q bits and clean the puller hole in the bolt body for a good fit. Take a few seconds to clean out the groove in the bolt where the extractor is located. After that, you can remove the bolt and pay attention to the extractor.
Assuming it’s heavily soiled, you may need a nylon gun brush to shake off the dirt so it can fall off the parts more easily. If it dries out too much, you can use RemOil or Hoppes Gun Cleaning Foam to make the job easier. Clean with a dry cloth, then use compressed air to remove any remaining detergent. While you are doing this, be sure to clean the top of the receiver where the BCG slides and where the charging handle slides.
Then you dip into the BCG and screw on the Rand CLPs and then place them on the end so that gravity pulls the CLP down for full and even coverage. This will help remove hardened particles in and around the bolt ridges and the like. You don’t need to disassemble anything to clean this area, just spray it with a degreaser such as brake cleaner or Birchwood Casey Gun Scrubber.
Do not oil anything after cleaning – this will only attract dust and dust. Make sure there is no excess oil residue after cleaning to avoid carbon deposits. Don’t worry about excess grease as it will collect carbon deposits and make subsequent cleaning easier.
Clean the center of the bolt head with a pipe brush and clean it properly. Once the hole is completely clean and dry, apply some lubricant to the clean patch and pierce the barrel with it. Use a rag to wipe down the firing pin so that there is no carbon deposits and make sure the tip of the pin is rounded and smooth for good shots – access the BCG body for signs of potential failure.
If the pins are tight or sticking, soak the bolts in solvent for five minutes before attempting to remove the pins. Remove the pin from the bolt (use a punch or striker). Press the latch into the buffer tube to release the buffer and spring.
To reassemble the bolt, reinsert the ejector and align the locking pin. Once the pin has been removed, the stripper can be slowly removed from the latch to avoid losing the clip.
After removing the CAM pin, the bolt can be pulled out of the holder. Most stop there, but we recommend disassembling the bolt itself so you can inspect the puller, o-ring and spring. Make sure the bolt is properly seated in the holder when installing the cam pin with the puller facing in the direction shown below.
The ejector has a notch for the pin and the ejector must return to the bolt in the same direction it exited for your rifle to function properly after reassembly. The bolt must be oriented so that the ejector is on the right side of the holder. The bolt must be pushed forward at the front of the holder for re-installation. The next step is to remove the CAM pin holding the bolt inside the carrier assembly.
Once the bolt is fully extended forward, you can turn the cam pin 90 degrees in either direction and pull it out. Reinsert the bolt head into the bracket body (you will see the bolt slide inside the bracket and rotate back and forth), once the bolt head is fully in the rearmost position, the bolt pin cam can be rotated 90 degrees in either direction. The cam pin must then be rotated about ninety degrees so that the rectangular head of the pin is parallel to the bolt bracket. Insert the cam pin of the bolt as you pull it out, turn it 90 degrees so it goes under the gas wrench, and insert the hammer into the back of the bolt.
If there is carbon deposits that prevent the hammer from slipping out (like mine), you can easily remove it by tapping the bolt holder on the table or pulling it out with your finger.
Only one of the two large holes on the side of the bolt is the correct size to accommodate the cam pin, so you may need to rotate the bolt to make sure the correct hole is used to insert the pin. Position the cam pin so the head is parallel to the foot body, then reinsert the cam pin. The cam will only move in one direction, so if it doesn’t fit the bolt, rotate it 180 degrees and try again. After the handle is inserted, make sure the bolt slides freely over the cam pin on the BCG.