Feb issue of swat has a right up on them. They did 60k rounds with only 2 springs and 2 screws that broke but otherwise, flawless. In one instance, they went 20k rounds without cleaning or lubing and no issues! I believe, as Darren at LWRC points out, 20k is 4 times the life of a bushmaster. Here's the link as there is some good info on them as they were shot to failure to improve the platform. Also, the m6a1 was used and new ones being shipped incorpate the new springs ect.
http://forum.lwrci.com/forum/viewtopic.php?t=3324
http://forum.lwrci.com/forum/viewtopic.php?t=3324