This is very interesting as someone I know bought 10,000 RIO 21g for his corporate days and has had quite a number of problems with them. My other friend helps out on these days and has told me of anything up to 6 faulty shells during a days shooting. I know I would send them back but I believe they were very cheap and they keep him happy by sending a few more each time it is reported. It just might be the cartridge and not the gun.
Phil