Oct 22, 2014

AR Buffers and Springs

Lower Receiver Schematic Drawing showing tube-buffer-spring assembly
Self-loading rifles and pistols require a recoil spring to cycle the action. The AR or military M16 is lightweight, therefore it requires a buffer that provides extra weight. The action energy is absorbed by the spring, so compression is important in order for the stored energy to push the buffer, carrier and bolt back in the forward position.
The buffer and spring ride inside a tube that is screwed to the rear of the lower receiver. The carbine tube is much shorter, except for the 'post-ban' stocks, and has a rib on it to guide the sliding stock. To remove the buffer and spring, push the rear take-down pin and hinge-open the action.
Plunger pin holds buffer in place
At the rear inside of the lower is a small plunger at the face of the buffer. Depress the plunger and the buffer spring will push the buffer out of the tube. Once the head of the buffer clears the plunger, grab the plunger and pull it and the spring out of the tube. Sometimes it takes some wiggling to get it past the hammer, which should be cocked.
Springs for the rifle and the carbine are the same diameter and made of steel alloy. The rifle springs have 41 to 43 coils, and the carbine springs have 37 to 39 coils.
If you have bought a used rifle or carbine and find that a spring has been shortened by cutting off coils, it should be replaced. If you find the spring has been shortened, it will need a complete inspection because other parts may have been altered, which is why the spring was shortened. You will have to find the reason why the previous owner cut the spring.
Springs also shorten with use. When a spring has gotten shorter than the recommended length, replace it. The rifle spring should be more than 12-inches long and the carbine spring should be more than 10-inches long. If they have shortened to those lengths or shorter, replace the spring.
Rifle and carbine springs should never be interchanged. In an 'emergency', one could get by by 'cannibalizing' parts from one firearm to another, but replace with proper spring as soon as possible. The longest spring found has been 50 coils long; which made the rifle frequently short-stroke and failed to eject. Counting coils is important when inspecting a newly purchased used AR series rifle.
The photo below shows the difference between a carbine buffer (top) and a rifle buffer (bottom). The bottom buffer is what you would see in military issue rifles. So the rule is: there is only one buffer that will work properly – six inches in length.
Photo by Gun Digest
For carbines, however, there are several buffers available. The shorter carbine buffer lacks the second spring shoulder found on the rifle buffer. Some carbine buffers are made of plastic instead of machined aluminum; indeed, if you have a lathe and the skill, you can make your own buffer as long as the measurements and weight are correct. Plastic buffers are filled with lead shot. I suggest you replace the plastic buffer with the aluminum so there will be no function problems.
A proper buffer is made of turned aluminum, 3-1/4 inches long, with a nail-like head (like in photo) and a plastic tip, which military rifles have a nylon tip that wears better. 
If you shake the buffer you may hear and feel steel weights inside banging back and forth. 
Buffer cutaway showing weights
If a carbine works properly with this configured buffer, no need to replace it unless you prefer to purchase a better quality buffer. If, however, you experience occasional malfunctions that you cannot figure out its origin, such as a failure to extract, and the extractor is bent or broken the rim of a cartridge, replace the buffer with a heavier one, like what Colt developed for military rifles. If you want to purchase something more economical, replace buffer on carbines with H or H2 buffers. In extreme cases, a carbine may require an H3 buffer.
Once again, never, ever, exchange buffers between rifles and carbines. If you use a rifle buffer in a carbine, the result, if you are lucky, will only be that the carrier key screws shear off. If the carrier screws do not shear off, or do so in a timely manner, the lower receiver will crack at the buffer tube threads. Then you will have to purchase a new receiver, which is more expensive that a proper buffer.
NoKick offers custom reduced kick buffers for the AR-15 and AR-10, for fixed and collapsible stocks. They are not cheap, the AR-10 Silent Captured Spring buffer system costing $130 to $140.
The AR-15 9mm buffer is available in a hydraulic model costing $125. The 9mm Silent Captured Spring system costs $130. A hydraulic recoil buffer is available for the fixed stock in AR-10 and AR-15 models. Buffers are available in stainless and tungsten.
The following video is informative concerning AR buffers springs ...
The next video covers buffers ... 

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