...galco has a specially designed cartridge wallet (with flap) for large bore double rifles (6 cartridges)...

...the leather is quite robust and durable, albeit not as 'refined' as, say, the leather products from westley richards...

...i usually just loop two such wallets onto a 2.0" safari belt (left + right) and unhinge each of the flaps during a hunt...makes for 12 easily accessable (and dirt protected) rounds...