check your guide rod. it may be slightly bent. roll it on a flat surface. not saying thats the issue just a possibility. the lip of the portion that contacts the base of the barrel could be bent too.
but that many rounds if its still got the original spring it needs a new spring.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
"I crapped my pants to avoid the draft!!" -Ted Nugent