What brand is it? Is it the Bushmaster Carbon15 or is it the Professional Ordnance Carbon 15 model? If it is a Bushmaster you did good. If it is a Professional Ordnance model you just got hosed on the deal. Most of the PO models were problematic with broken bolts and no one services or repairs them. Bushmaster will sell you all the parts to modify it to make it work but the they will not replace individual pieces to fix it if it were to break. The info is posted on their website under FAQ and all the newly modified parts are available to get it back into service, basically it calls for a new barrel, gas block and other items.