FYI folks can probably be more helpful if you give more information. What ammo? Have you recently changed ammo? How often do you clean the gun? Does it happen every time, or only sometimes? How old (approximately how many rounds fired) is the gun? Has it always done this or is it something new? If it once shot well did it get worse gradually or did the problem start suddenly? Do the cases extract partially from the chamber, or are they still fully seated? (Actually, this might be difficult to determine if the next round is striking them and driving them back in.) Does the fired case extract easily or does removing it require tools?
@Hawkey probably has the right of it...but if it's something that came on gradually and especially if the fired cases are difficult to extract I'd put a close eye on the chamber, too, as a bur or or very dirty chamber could have led to damaging the extractor.
John