Buffer Spring
http://www.davidtubb.com/tcom_images/ar15_images/cs_buffer.html
Speaking of buffer springs check these Chrome Silicon Springs.. North Dallas and myself use these and they are great. First they get rid of the mechanical sound coming from the compression of the spring when firing and they will last for 500,000 compression cycles with a loss of no more than a quarter of an inch. Standard springs are rated at about 5,000 cycles. When I replaced my spring it was durn near inch and a half shorter then the new one.. Bonus is they are not that much more expensive then standard springs...
