Wednesday, June 13, 2012

AR-15 Bolt and Carrier Basics

It is important to have some basic knowledge about the AR-15 in order to enjoy the weapon and keep it functioning to its full potential. The AR-15 is a fairly simple weapon to keep clean and maintain, as far as semi-automatic weapons go.  In this post, we will go over some very basic information about the bolt and carrier assembly, including dissassembly and maintenance. 

Most AR-15 rifles will have either an AR-15 or M-16 bolt carrier.  The bolt will be the same in either instance, but the M-16, or "full-auto" carrier is a bit heavier than the AR-15 model due to its design.  There is a larger "cut-out" at the bottom of the AR-15 model.  While an M-16 carrier alone will not make the weapon full-auto capable, some AR owners believe that having the heavier M-16 carrier is beneficial in carbine gas sytem rifles; it is thought that the extra weight can slow down the cycling of the weapon.
carrier and key assembly

The standard, mil-spec carriers sold at DTI have a chrome lined interior. A fully chromed model is also available. Coatings like chrome, titanium nitride (TiN), nickel boron, etc... can make the parts easier to clean and provide lubricity and wear resistance.  A standard, phosphated, mil-spec carrier will work fine and can provide the average owner with a lifetime of service if it is properly maintained.
Atop the carrier (3), is the carrier key (2) that also has a chrome lining.  The carrier keys used in DTI products are attached with grade 8 carrier key screws (1) and the key is "staked" according to military specifications.  This involves making an indentation in the metal of the key on both sides of each screw in order to preven the screws from easily backing out during normal operation of the weapon. 

At DTI, we use bolts machined from carpenter 158 steel. Each bolt is then high pressure tested and magnetic particle inspected (bolts used in the DT Sport line of rifles are not individually HPT/MPI tested, but are made of the same material on the same machines as the bolts that do undergo this testing). The bolt is used to fire a high pressure round of ammunition (HPT) and then closely inspected (MPI) to search for any fissures or imperfections in the steel that may have resulted from the force of the excessive pressure.  Factory ammunition is loaded with powder that creates pressures well below the those created by the HP rounds, so a DTI AR owner can feel confident that our bolt has the quality and integrity to provide functional and long-term usage. 
There are many opinions on what is necessary in regard to cleaning and maintenance of the bolt assembly, but it is definitely important to remove the bolt from the assembly for cleaning each time you clean your weapon. Doing so will only help keep things functioning right. 

To remove the bolt from the carrier, first remove the firing pin retaining pin (1) from the carrier. Once this is done, the firing pin (2) can slide out toward the back of the carrier, and the cam pin (3) will rotate properly for removal from the bolt. The bolt (4) is then free to slide out of the front of the carrier (5). 

While the entire bolt should be gently cleaned, the "face" of the bolt, the tail end of the bolt, and the firing pin will likely have a fair amount of fouling and carbon build up that may require extra attention.  Any solvent or solvent/oil cleaning solution can be used for cleaning.  A firm, nylon bristle brush or dental pick may even be required depending on the amount of fouling that has built up.  The pick can be used to ensure there is not a build up under the extractor as well.  All external and internal surfaces of the carrier, carrier key, and cam pin should also be cleaned.  Cotton swabs or pipe cleaners can be useful to get into the small areas, but there are some manufacturers like Iosso that make specialized nylon brushes for this use as well.  The exterior of the bolt and exterior sides and bottom indented rails of the carrier should be lightly oiled before the entire assembly is inserted into the upper receiver.
Iosso AR-15 cleaning kit

Cleaning after any shooting session or prolonged storage is always a great way to provide a long life for your AR-15.  For additional information on this post's subject matter, please visit our retail, you can also view exploded diagrams of these parts. If you have any questions about AR-15 bolt and carriers, DTI rifles, or anything about the AR-15 in general, please feel free to contact us.

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