If you play a lot of hardcore and want to get back to core, the best way I go about it is to take a break from the game completely. For about 3-4 days. Then when you finally play again, you just go straight to core and it'll feel "normal", if you know what I mean.
But when you switch between the two modes, core just seems ridiculous when the halo jumping, drop shotting, etc all save them from dying. --- Anyone who supports DLC of any kind deserves a swift kick to the balls... repeatedly. Take a stand! Don't let companies take advantage of us!