If it's "Make ready!" time, I can load either way and use my eyes to confirm the mag catch is back in fully seated position (indicating catch is hot). I'll rack and do a "pull check" to make sure there's a round in the chamber and give the FA a couple of taps just to make sure. These are superfluous in most cases, but everything's off the clock at this point.
If it's in the middle of a timed stage/run, I'll generally keep my eyes towards the target and slap the bottom before I hit the bolt release. I try to remember to clean the mags every other time I clean the rifle, and have never had any trouble loading (and discharging) a full 30. With either 20 or 30 rd, I've gotten used to pulling and holding the mags like I do pistol mags, with my left index finger along the front edge and the mag bottom against the heel of my palm,....it makes pointing at the magwell more intuitive and ready to slap. Just my .02
Then again, I'm not at the round count that wears out springs and sundry parts every season, either.