"RG GUM" ???

"Maybe there are few versions of 380 me gum - in Lithuania we can buy these - it is said that their power is lower than 7,5 J, but nobody knows exactly"

I don not want to break your country's laws. But.

If this loooong cartridge fits into a chamber, you can load it with normal 9 mm Knall+10 mm rubber from the rear, and shoot it out with 30-50 Joules depending on the gun and knallpatrone.

If it is illegal, just forget it.

(I suppose you have the same revolvers as Russians, but differently loaded ammo.)

I guess i will have to forget it
Some people use me 38 in this way, but it is illegal. And then the revolver lasts only 30-50 shots.
There was makarych (the makarov version shooting rubber bullets) in our gun shops (dont know how it was imported in Lithuania, maybe as gas pistol), but there were no cartridges for it and it was very expensive (legal Makarov, combat pistol, is cheaper).