Quote:
I would still only load the first two shells in an 8 round tube with such ammunition and have the rest of the tube loaded with the real thing

Seems sensible.

Examples of non Lethal ammo sold in France
On the same site, you can see some handguns using those ammo.

French laws : anybody can buy the 12/50 cartridges, filled with rubber buckshot (12 small rubber balls - ref GC27C on the mentioned web page). But you need a special permit (the same you need to buy a .357 handgun) to buy the 12/50 cartridges filled with 1 single big rubber ball.

As for being non-lethal : the manufacturer of both those 12/50 cartridges recommands on the packaging not to use them under 5m.
That doesn't prevent the retailler to mention on his web page "High stopping capacity up to 4m." !!!!
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Alain