Are you jumping with US Mil?
Something you may be interested in
http://supplycaptain.com/index.cfm?f...product_ID=134
Closed top when you want it to be, and the flap can be tucked behind a piece of webbing in the pouch(making it even more tight) or removed completly - still tight. You won't be loosing mags from these pouches. This pouch AFAIK would be jumpable.
I have 2 in Coyote Brown for sale also, check out link in my signiture.