I was recently fooolin around in single player, and hit a 6 dm boom, which I though was pretty awesome.

So I saved the replay, was going to edit it later. Now, I come back to it, and it's only a 3 or 4 dm. And, if I edit the replay right before the 3-4 dm boom, and just let it play, then it's a 6 dm boom again. Check it out.

Any help?

Play the replay till after the hit and save it again. You probably moved a joint before the hit that you saved.