How reckoning is currently scripted is completely wrong, an example of how it should work can be found in Loke 2 a famous pally vid from vanilla.
In this video at 0:20 he attacks zeromancer with a few stacks of reckoning, he then targets himself while gaining more stacks (changing target), then aggressively targets zeromancer again at 0:24 while being out of range of auto attack swings (shown by the messages on the screen), he then casts Hammer of Justice, then moves into range to and unleashes a reck bomb the second his auto attack is in range, without him losing any stacks due to being out of range or changing targets.
This is not how reckoning functions at all in classic, if you are out of range you lose your stacks, if you change target you lose your stacks and now for no reason at all you lose your stacks.
You then see him target himself again and then unleash another reck bomb at 0:34 seconds.
again at 0:52 seconds and then at 0:55 seconds without disabling auto attack he unleashes a full reckbomb on the warrior the second his next swing is up…
The current version of reckoning isnt even close to accurate and needs massive overhauls… just look at actual footage of the game, rather then making it up on the fly.
Further references of how reckoning should actually work can be found throughout the video as it shows again and again how the talent should actually work.