Although I no longer own a .223, I still have the Harry Owen .22LR/.223 blued steel chamber adaptor I used for awhile in a T/C Contender.
The accuracy was commensurate with the normal accuracy from that gun - no better, no worse.
The rate of fire, however, was a lot slower because once the .22LR was fired and the adaptor extracted - the fired/empty .22LR case still had to be poked out & reloaded before the adaptor could itself be reloaded into the gun's chamber for firing again.
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