Guys, just an aside here...
When I shoot handgun, I put a tarp down. The mags hit the tarp (along with a bunch of brass, which is now easier to pick up). Same with brass and speedloaders from the .357. Yeah. I drop 'em when they're empty. How else am I gonna shoot the boomstick?
If I have a mag in the pistol, and two in the pocket, I'm not worrying about "is it disposable?" I'm worrying about putting as many rounds into the bad guy(s) as possible, until they stop moving toward me. Hence, that sucker hits the ground, and hopefully while it's still in the air I've got another round in the pipe.
If you -train- being careful, you'll -fight- being careful. Magazines are not disposable, but they are consumables.
Remember - I think there was at least one cop in that Miami shootout who died with brass in his pocket, because he didn't dump and speedload - he'd been taught to carefully pocket the brass.