They're made by, I believe, Bianchi.
Basically they are a rubber strip with recessed and lipped cutouts into which you snap the rims of the cartridges.
The cartridges are held in a straight row, meaning that it lies flat in a pocket.
To use, you insert the cartridge into the chamber, and twist the speed strip to "peel" the cartridge out if it.
If you practice, you can load two chambers at a time.
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Beware the man with the S&W .357 Mag.
Chances are he knows how to use it.