I spent some time behind an early Surgeon CSR prototype at a class taught by Pete Gould, Pete had taken that rifle down range when he was at USASOC and made recommendations to Surgeon that ended up in their final production version for the unit and I didn’t ask if he bought it from Surgeon but I got the impression that they just gave it to him. Anywho to make a short story long Pete explained the concept and function of the CSR between range sessions and he had a IIRC 14” 308 subsonic barrel that I think was a 7_ twist and a 20” 308 barrel for M118LR, both barrels had wrench flats machined behind the muzzle threads and he could spin one barrel off and another one on in about a minute depending on the application needed. No special tools needed and he tightened the barrels barely past hand tight and said that he had tightened them just with his hands and saw no POI shift
Interesting that you mention the hand tight barrel torque. A close friend of mine has an original Surgeon CSR that was a contract overrun rifle from the first 100 made (long before they changed the model designation to the SRL and used a different chassis), and he only hand tightens the barrel ti the receiver each time he brings it to the range, lol. I guess it's okay doing it this way because it's still an extremely accurate rifle and he's never had any issues with it. The Remington PSR/MSR/CSR rifles all use a torque wrench set for around 20 foot pounds to tighten the barrel nut on those rifles.
Just like you mentioned about the Surgeon CSR, the Remington CSR was also specifically designed to shoot .308 subsonic ammo out of the 14.5" and 16" barrels (prototypes only, the civilian production 16" barrels had a different twist rate to use with typical supersonic off the shelf ammo). The prototype Remington CSR's had a maximum effective range of 300 yards with custom loaded subsonic ammo and appropriate barrel/twist rate. The Remington CSR's were actually developed for a certain Army unit, not SOCOM or DEVGRU, like what published information typically says. I recently spoke with one of the guys who worked on the Remington PSR/MSR/CSR programs, and he verified that the Army wanted the Remington CSR rifles. I also asked a Navy SEAL friend about this and he verified that information. Some of these rifles eventually made there way over to SOCOM and some SEAL teams, but they were originally supposed to be used for secret squirrel Army plainclothes work.
I really appreciate you posting actual first-hand information about the Surgeon CSR prototypes! That's a very interesting rifle and even though a decent number of them were actually used when they were finally put into limited production for the contract, not too much is known about them. Even photos of military issued Surgeon CSR rifles are very rare! Do you have any photos of the prototype CSR rifle that you got to shoot? Any new photos/information on that platform is appreciated!