I'd call Ruger & ask them. IF - they'll do it, the new cylinder has to be fitted to your gun. You can't just get a cylinder & expect it to work.
The chambers have to line up perfectly, the barrel/Cylinder gap has to be within spec etc.
I know this because I bought a BH 45 Colt & after the purchase found out about convertibles. So I contacted Ruger & this is what they told me.
By the way, If your gun never came as a convertible, Ruger almost surely will not make it so.
Good luck!
I started the process by email & here's what they said about my BH 45 Colt.
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Response:
Cylinders are a fitted item to each individual firearm and need to be installed by our technicians at the factory.
Cost for cylinder installation: $95.00 for the cylinder, $50.00 labor and $30.00 return shipping.
Thank you for your interest in Ruger Firearms.
If you need further information, please visit our website at
www.ruger.com or contact us at:
Revolvers, shotguns, rifles, 10/22 Charger Pistol: (603) 865-2442
Pistols: (928) 778-6555
Serial Number History Information: (603) 865-2424
Please note: This e-mail is sent from a notification-only address that cannot accept incoming e-mail. Please do not reply to this message.
Sincerely,
Ruger Firearms