I have an old 22RF rifle that I would like to convect
From reading this, I get the impression that you have a 22 WRF and want to convert it to 22 WRM. Is this right? If so, you just need to ream the chamber to 22 WRM dimensions.
If instead the rifle is chambered for 22 Short, Long, or Long Rifle, I would recommend you find a different project. 22LR has a smaller bore than the 22 WRM, which will cause pressure issues.
22LR and 22 WRM share the same SAAMI max pressure rating, 24,000 psi.