One round for every second of the minute
Magpul’s D-60 is billed as a durable, lightweight, highly reliable 60-round 5.56×45 NATO/.223 Remington polymer drum magazine for AR15/M4 compatible firearms to include the M16, FN SCAR MK16/16S, HK416, MR556, M27 IAR, IWI Tavor, and others.
I got my hands on one back in August and have been kicking it around for a few months to see how it held up.
Full review in my column over at Guns.com (with a bunch more pictures and technical specs etc).