One of the weakest links in the AR system is the extractor. Not enough tension and the weapon will not run properly. Crane came up with a rebuild kit for worn out springs and inserts along with an O-ring to help with extraction.
I have also installed this upgrade kit to the CMT MP tested bolts we sell.
Please e-mail us with any questions. sales@grtactical.com
C4
Crane O-Ring Upgrad Kit is available here: http://www.gandrtactical.com/cleaning.htm
CMT MP Tested Bolt w/Crane Upgrade Kit installed is available here: http://www.gandrtactical.com/cmt.htm#pMPI