Your timing is off and you're probably not canceling the LP. Learn it on Kano first because he's easiest to do it on then Jax, then Kung/Kabal and followed by female ninjas. I say it in that particular order because those characters get hit by the gun higher in the air and make it easier to juggle them. Other than that the only real tip I can give you is practice, practice, practice.
The spacing from the corner has to be the right range. pop up, deep jk, lp, gun, jk, lp, gun and so on. you have to pause a little between the lp and gun. So the LP pushes you out of the corner and sets you up for your next jk.
hope this helps. Look up some stryker corner inf vids as a reference.
Yeah, most of the time I read the guides(if I use that character) to see if I can learn something new I don't already know but if there's threads like these, figure why not just ask since someone will answer fast. 8)
I also could just ask shock since him, DED literally know everything about the game but don't want to bother him with such a small question unless I really want to know what works, what doesn't etc.