Our new D-Fender "D-Ring" can assist in eliminating extraction problems in the M16, M4, and AR15. This High-Tech, composite "D-Ring" increases extractor spring force by 4x! As chamber pressure increases from gas-port erosion, you will notice an increased cyclic rate when firing in full auto (less apparent when firing in semiautomatic). Along with this increase in pressure comes a much faster unlocking of the bolt, meaning that it is turning much faster than normal. The fast spinning bolt creates a centrifugal force causing the extractor to open prematurely and therefore not properly extract the case from the chamber. This has been a problem since the beginning of the M16 weapons program and has often been misdiagnosed by gunsmiths and armorers as chamber problems, carrier-key problems, or gas-ring problems. Years of testing and evaluation have gone into the D-Fender project. The material that the D-Fender is constructed of will not break down under normal weapon operating temperatures, nor will it melt from cleaning solvents and lubricants. It will not become "squashed" from the pressure of the extractor, or become dislodged causing the weapon to malfunction. We mention these particular problems because we have heard of several people trying to substitute the inexpensive hardware store variety "0-Rings" for this use, and these failures are a result of that practice.