Luger .05 calibre insert barrel
 

I have a chance to buy this. What do you think and what is a fair value?

It is described as

05 calibre barrel insert for Luger handgun.
Originally designed for target shooting in the home during pre-war times.
Includes original box and 10 rounds of .05 calibre rim-fire and loading tool.

Thanks

Nice set. Ammo is called 4mm M20.

This design is the single shot, after which one pokes out the empty case with a special poker? Weren't there several versions of the single shot conversions. Is this one German or Swiss? Please tell us more, Gerben!

Yes, these were designed to use indoors, so one could practice with a service pistol without having a complete shooting range available. This set looks like it is the Erma version, similar sets were marketed by RWS and Lienhard. The set has the loading spoon but is missing the poker/cleaning rod. Usually the spoon is missing.

The 4mm M20 was based on an earlier 4mm rimfire round. The 4mm M20 has the advantage that it functions both as a centerfire and rimfire version, so it is easier to build training sets around it. The rounds hold no powder, the small ball is driven out by the gas pressure of the primer only. They are relatively accurate up to about 15 meters. I shot at 25 yards as well, still a nice punch hole in the cardboard target.