the block is catching on the frame ,just press the leaver obove the triger it will straiten and you will get it back in easily,wile it is apart get a fine stone and take of any sharp edges this wiil smooth things up a bit,they get smoother with youse,i jus noticed you have one of the early ones with the loose extractors,the extractors only fit one side each the tabs face in( they are the extractors)the long pert of the slide faces towards the botom of the action ,put it together the wrong way and it will not go back together,also if you conpress the block(just put your finger between the leaver and the lower block to hold down and it will go back in much easier