I recently purchased one of the rifles and I love it. Really fun to shoot and just neat. During a detailed cleaning after about 400 rounds, I noticed a crack in the black plastic block that appears the be the buffer block where the bolt slide rails are located. I called S&W at 1-800-331-0853 ext 2905 about it. Mine has 3 small cracks in the plastic. The one that would concern you is in the groove where the bolt buffer spring sits. Mine and my neighbors both have cracks in the same place. I will be sending mine back, prepaid after I get the packet from them. If you have one, you should look. The main one is in the top in the face of the block. It is also visible under a mag lite when looking thru the back side. There is one in the bottom of the groove that the spring rod mates up to, and on mine, there is one behind the area on the face near the bottom showing from behind the stamped metal that is the bolt guide rails. Seems like if the one in the spring groove got big and spread, the buffer spring would pop out of the groove. Best to take a look now.