you're going to have to drop the trigger assembly out and also take the bolt out. There is clearly something hanging up in the action. Aside from cleaning, also inspect the trigger group assembly. There are pins thats are held in by horseshoe clips that may have fallen out. By the looks of it, it appears that the shell riser is hanging up and jamming the bolt. As mentioned in the previous post, look for any marks on the bolt and trigger assembly to pinpoint the issue. This should only take you a few minutes to see whats going on. Drop out the trigger assemby first and rack the bolt a few times to see if its hanging up without the trigger in the action. If it does, take out the bolt and inspect. If it doesnt, then the issue is likely in the trigger group.
If the gun worked well in the past, and this problem is fairly new, then when did it start to happen? If it started after you gave it a cleaning, then its certainly possible that something occured in the trigger assembly during the cleaning process, and you may not have caught it. I have a Mossberg 935 and if Im not carefully when cleaning the trigger group, there are roll pins that could fall out of the trigger assembly. If I remember correctly, one of those pins may be the trigger hammer pivot. If that pin fell out, that its possible that the bolt of getting hung up on the hammer.
