Phil:
Here's a fairly comprehensive thread dealing with this subject a while back:

Previous Thread

Lately I've been "field testing" a flop-open ammo wallet made by our very own talented saddler Al McKenzie. It holds 8 cartridges, stitched in pairs, and is equally at home with .400 Jeffery, .470 NE. and .577/.500 No.2.

Very happy with its performance so far!