I use the Inertial puller to lengthen any rounds that are too short (and by too short, that's usually a thousandth outside of the range of lengths I allow for myself when I start), and occasionally I have to pull 50 or 100 when I decide to change the load. Just tighten it up (I wear a glove, as tightening/loosening the cap gives me blisters after a dozen or so), then re-cycle the powder (as long as you are using the same powder), bullet, and brass.
After a practice, I often wind up with the rounds that have popped out of dropped magazines. In that case, I discard the powder (can't risk mixing the wrong powder with mine).
To discard powder or primed cases, I put them in a large peanut butter jar, and fill with WD-40, just enough to cover everything. AS time goes by, I add more to it, and add more WD-40 as needed.
Also, after a practice, I volunteer to take the rounds that have popped out of dropped mags. Inertial puller, discard the powder unless you were the only o