I have a 1945 Remington Rand with a Colt 45 Auto barrel with a "S" on the bottom. These "S" barrels were used in 1943 Colts and possibly in the early 1943 Remington Rands.
If the premis that were were used in the 1943 RR's is correct, would it not be possible that some leftovers came out of the woodwork and were used in 1945 RR"S?
Of course, all this is to justify the fact that my RR is correct.

What say you experts??

Colt did supply barrels to Remington Rand during initial startup before High Standard got into barrel production for the 1911A1, but in case High Standard barrels were not availalble any additional barrels would have come from Flannery Bolt. You could consider it correct, but you would have a hard time convincing anyone else that it was correct to the pistol.

I think the only Remington Rands I know of with Colt barrels that are believed to be original are the very early guns. And I don't recall any of those being the Colt S marked barrels.
Does your barrel have the P proof on the left lug? If not, is strictly a commercial barrel in the first place, and would not be considered correct in any of the military pistols. If it does have the P, that would indicate the barrel was proofed for military use, but certainly not necessarily in that pistol.
I'd suggest looking very closely at the back end of the barrel... on the back of the hood and the back edge of the chamber area. Then, compare the precise wear patterns found there to those found in the mating areas on the recoil plate of the slide to see if they match exactly. I suspect the wear patterns will not match exactly, or you may see some matching patterns and some additional wear patterns that don't mate up.
The additional non-matching wear patterns would be showing the wear pattern of a previous barrel in the pistol that has since been replaced.
You can also look at the locking lugs for signs of wear; then look on the mating surfaces of the slide for the same signs of matching wear patterns.
This will work on pistols that have been fired some, but will not work on pistols without any established wear patterns.

Sounds to me you have a 1911 WW1 springfield armory barrel, if you are looking to get rid of it for a original rr i am interested. I have a S.A WW1 and no original barrel

It is definitely a Colt barrel not a springfield

Well, ive been wrong once or twice before haha, so ill take your word for it.