Which model of RG? They made a few different 6-shot .22 revolvers. The RG10 was .22 Short only (although mine chambers Colibri's quite well), the RG10S was it's .22LR counterpart, the RG14 and RG24 were both .22LR swing-out cylinder models, etc.
It does sound like you need to clean/polish the chambers though. There may also be some peening on the chamber edge (where the cartridge rim fits) due to someone dry-firing it too often.
I usually shoot my RG revolvers with either CB's or Colibri cartridges just to keep down the wear and tear on them. Yes, I collect and shoot SNS pistols of all sorts....it's a sickness that I enjoy.
Jack