I see
@LakeTrout already answered this. I generally only fly Southwest so can’t comment on other carriers, but SW does not allow loaded mags, only authorized storage containers as noted.
One time I was flying from Texas to BOS and one of my cardboard boxes had got soaked and fell apart during my trip, so I just stuffed the 50rds into a sock and tied it off. About 30mins post security I was called on my phone by airport police asking if they could come meet me about some ammo.
The guy was cool about it, came to me and didn’t make me f*** around with security again, just wanted to let me be there when he opened the bag again to remove the ammo in a sock and explained SW won’t allow it. Anyway he wasnt busting my balls or being a dick about it, I never ID’d myself as LE fo him, just another Joe Blow and I was off again in like 3-4 mins to my flight, albeit 50rds shorter.