Caldwell of Battenfeld Technologies has released their AR-15 Mag Charger system, designed to work with 50 round boxes of 5.56/.223 to load magazines quickly. With ammo in the charger system, each push of the plunger, the charger loads 5 rounds and advances the feed tray to the next slot. A 30-round magazine would take 6 charges to be loaded to capacity.
The Mag Charger is compatible with all AR-15 magazine systems. Their demo video shows the system being used with SureFire 60-rnd and Beta C-Mag options. No word if the system supports similar-sized cartridges such as 300 BLK, 6.5 or 6.8mm.
The unit retails for $89.99, but is available for less from prominent retailers.