Bolts need cleaning, both inside and out. Everyone will clean the outside and put some grease on it but few take the time to remove the firing pin assy and make sure the bore of the bolt hasn't filled with crud. For those who haven't had it happen consider yourselves lucky. For those that want to make sure that the rifle is 100% reliable, a periodic internal cleaning is in order. You don't have to break the bolt down to all it's component parts, but at least clean the firing pin channel and inside bore. Flush any crap that has accumulated on or around the spring off as well. A small amount of lube on sliding surfaces is all it needs when it gets reassembled.