I was wondering what is the most rare of carbines?

Commercial Controls, only about 230 made. Mikey

What about the original T3 sniper version, only a couple of hundred made before they just started converting stock M1/M2 models?

You could be right Jester. I'm not sure how many of those were made. Do you think this is one of them, or one of the later versions.

The T3 versions were marked T3 on the left side of the receiver and I believe were all Winchesters. The lower rifle in the photo is either a T3 or an early M1/M2 conversion as the IR source is below the barrel. They abandoned that design in favour of the source mounted above the intensifier as to use the IR hung below the barrel the 'sniper' had to rise out of cover to unmask the beam. It is also missing the later flash hider.

The upper rifle is unusual, could be a comercial post war conversion, but there were also several versions made up by armourers using the 1.5-3.5 power spotting scopes mounted on antitank guns during Korea. None of those versions were ever 'officially' sanctioned but sure would be a nice addition to a collection.

The last T3 I saw for sale on GunBroker in the US had a reserve of $US13,000 and sold for $US15,500!!!!!!!!!! It will be a long time before I have one of those in the collection, though the meserly $850-1000 for a hand in to import it will be insignificant at those prices!!

Just had a look in "War Baby" (the book), the lower carbine probably is a T3, the "in the field" sniper modifications had a band that went around the foregrip and over the top wood to help secure the forward pistol grip/sight switch.

Jester, I just checked out that book. Page 233, Inland produced 811, Page 235, Winchester produced 1,108. I beleive these to be the original ones and are they are not as rare as the 239 ordinary M1s produced by Nat Postal Meter after they changed their name to Commercial Controls. However, I always stand to be corrected, to live and learn. War Baby Comes Home deals with all the later T3's. It's great to meet you, I hope we can help each other. I'm Mike, Wellington.

"...Commercial Controls, only about 230 made..." That's not a U.S. military contractor.
Of all the official manufacturer's, Rock-ola made the fewest. 228,500.
Inland(GMC) made 2,642,097.
Winchester. 818,059.
Underwood. 545,616.
Saginaw(GMC) 517,212.
National Postal Meter. 413,017.
Quality Hardware & Machine Co. 359,666.
IBM. 346,500.
Standard Products. 247,160.
For a total of 6,117,827.
There were over 1600 sub-contractors making parts all over the Eastern Seaboard of the U.S. Only IBM and Quality made most of their own parts.
This doesn't include any of the post-war commercial manufacturers.

Rock-ola did not make the fewest carbines. I depends on how you define manufacture, prime contractor, and contractor. The rarest (least made) receiver manufactured is Commerical Controls, abt. 239. They were the new name to National Postal Meter and were a contractor since the military accepted their receivers. The rarest prime contractor is Irwin-Pederson, abt. 50,000 recievers. The rarest contractor is Saginaw (S'G') (Grand Rapids) who took over for Irwin-Pedersen. They made less carbines than Rock-ola, abt. 214,000.

Winchester made the most parts themselves. Quality Hardware & Machine Co. was an assembly point of parts prior to becoming a prime contractor. IBM also sub-contracted many of their smaller parts.

Models of carbines (M2, M3, M1A1) are not as rare as presentation and experimental carbines. Some of theses carbines can be unique and the rarest.

from what a have read rock ola and winchester made the most them being the only ones to deliever a full carbine but iam not sure