I have experience of 6 different REM 700. Made from 1972-2007. Calibers; 270Win(2), .30-06(2), .35 Whelen & 7X57.
The .270'S were a RT & LT purchased from the same dealer on the same day from the same shipment in Aug 1974. They both shoot well with the same load of LYMAN #280442 & a light charge of UNIQUE. With Jacketed slugs it was a whole different story. One load would give 1 1/2" 5 shot groups in one rifle & 3" groups in the other. Ended up with 2 completely separate loads for jacketed & just 1 load for cast.
The ought 6's (1972 & 2007) both shot well with #311291, #311407, 311413 & 311329. With a #311407 sized .309 cast of LINOTYPE & lubed in EVERY groove coming out the best. A light load of UNIQUE shot best, with SR4759 for a heavier load. 1 1/2" - 2" 3 shot groups being the average for either gun.
The 700 Classic's were a different story. The .35 Whelen shot well with both bullets cast of LINOTYPE, sized .358 DIA. 50yds with a #358429 over a light charge of UNIQUE . It made a good bunny load with one hole groups at 50yrds. For a heavier load , I found an old Lyman small block single cavity mold; #358009. Dropped at about 240grs. I used H4895 behind it to start. Decent 3 shot groups 2-3" at 100yrds. But only on good days & from a VERY CLEAN barrel. Every gun is a law unto itself.
The 7X57 Classic; my tried & true #287405 failed me completely. I had that very Kind & Extremely Knowledgeable Gentleman, Mr. Joe Penny make me up 4 different cast bullets. I tried at least 4 different powders, including my favorite Unique. Couldn't find a cast load that would group 3 shots under 4 inches. It shot OK with jacketed but I never found a cast bullet load worth an ounce of lead.
There's my experience, just don't ask about Model 70'S, pre or post. Shot just a couple when I was a kid. Never had Ruger M77's in a caliber that I had molds for at the same time, so I never tried cast in one. I learned all this from my Dad, with old LYMAN manuals, supplemented by the newest LYMAN manuals available.
Long time Caster/Reloader, Getting back into it after almost 10yrs. Life Member NRA 40+yrs, Life S.A.S.S. #375. Does this mean a description of me as a fumble-fingered knuckle-draggin' baboon. I also drool in my sleep. I firmly believe that true happiness is a warm gun. Did I mention how much I HATE auto-correct on this blasted tablet.