Originally Posted by Rhamma
Any standard 1911 mag should work. As far as I know Remington Rand did not make any magazines, just the pistols. If you did find a original Remington mag it would more than likely be a collectors item and you would pay as much for one Remington mag as you would for several aftermarket magazines.
More than likely your barrel has not been throated and your feed ramp has not been polished. PLEASE, do not have any mods done to this pistol!!! Leave it exactly like it is, it has definately seen your grandfather and father through the night and proven itself.Keep in mind the military only shhots ball ammo through their pistols. That pretty much negates the need for ant reliabilty mods.
What I would suggest is find a company that sells GENUINE GI mags, you can usually purchase quite a few of them fairly cheaply. Take your mags and your pistol out to the range, take a sample of the ammo that you intend to trust your life with. If you have a single malfunction with one of the mags, ditch it or reserve it for range use. Keep the ones set aside that you don't have any malfunctions with and keep these for real work.
What type of ammo are you using? Speer Gold Dots have a nose profile that closely resembles a FMJ round, so they tend to feed on a reliable basis.