Let me refresh my memory. FIE is or was Firearms Import Export Corp.They were in Hialeah Florida. In 1990 they became QFI(Quality Firearms Corp.)when most of FIE's models were discontinued and are located in Opa Locka Florida now.FIE were very cheaply made guns. There were different models. The Arminius were a pot metal d/a revolver. These were made in 22,22mag,38spl and the 357 mag.
Other models were. Buffalo Scout,Hombre s/a rev.,Little Ranger,Super Titan II(semi auto),Titan Tiger d/a rev.Model TZ75 d/a semi auto and probably the one you have the Texas Ranger which were made from 1983-1990. They did have a convertible model in this Texas Ranger.Since they made the convertible model your cylinder should be long enough to accept the 22 mag cartridge. It would have to be reamed by a gunsmith to take the mag cart.It would probably be more then it's worth.This is probably not what you wanted to hear about these FIE's.They were probably a little better then the RG's(Rohms)but not much.I lived in South Florida and worked at a local gunshop for awhile.The shop I worked at refused to carry FIE guns because they were so cheaply made.Universal Firearms were right around the corner too.They turned out allot of MI Carbines.They are probably gone by now too.
If you want a S/A Revolver Convertible invest in the Ruger Single Six.
Ruger Redhawk

..... A Proud NRA Life Member since 1977 .....Ruger Redhawk