Loading a Double Rifle quickly

[IvW]

2 cartridges in the palm of my left hand, break the double holding the rifle with the trigger hand, two new cartridges go straight in from the left hand and the shut the rifle.

 

[towserthemouser]

Speedloader Swift

Anyone with good 3D printing skills might be able to make up something similar for use with big bore rifle cartridges......

Any thoughts?