The Rohm or RG revolvers were made in West Germany. They are low cost handguns of indifferent quality. Value would range from $25-$70, depending on condition.
the caliber is stamped on the gun.
The short answer is no. The longer answer is, you may be able to get a .25 cartridge into a .22 caliber gun, but it will likely jam and be very difficult to get out, and if it fires, it will probably damage the gun and possible the shooter. The .25 has a larger diameter than the .22.
Inexpensive hand gun.
The answer to the question is no. A .25 is larger in diameter than a .22 so it won't fit into the chamber. Beyond the question, you should never try to insert or fire a cartridge in any gun other than what the gun is designed to fire. If you do get it to fire, it may cause damage to the gun or the shooter.
who invented the six shooter hand gun
you will have to go to gun shows and gun shops.
Gun range rental fees in the United States of America generally cost between five and twenty dollars. The caliber of the gun greatly influences the cost of rental.
There are several manufacturers who make or have made firearms in that calibre, and cost varies greatly.
the 12 guage is a caliber not a gun
Stevens 30 caliber rim fire is not a true 30 caliber. Chamber is .296. Bore .270 t0 .277. I found a 30 caliber rim fire round, at a gun show. It did not measure out to a 30 cal. Shot shooter
John Hinckley used a .22 caliber revolver to shoot President Ronald Reagan.
RG is short for "Rohm Gmbh" which essentially is Rohm Ltd. in German. Rohm manufactured inexpensive (and somewhat questionable quality) handguns until 1986.