YES,in the search for a case with the potential to replace the .30 -06, the .300 Savage was selected as a starting point, as it had the same head diameter; the Savage was a 7,62x47 ; the 30 cal a 7,62x63.
By experimentation they arrived at 7,62x51 ( at the same time, Britain and FN also trailed a 7mm cartridge of similar dimensions, but circumstances forced them firstly to adopt the .30 cal case Head diameter, then eventually the 30 cal. bullet ( 7,62).
The mention of the 8x50R and the 8x56R is a non-sequitur…ie, ofno comparison. The 8x56R was developed as a MG cartridge in the late 1920s, to improve the performance of the M93 Round nose cylindrical 8x50R cartridge, without having to adopt a new Rifle design from the M95 Mannlicher, or M1907/12 Schwarzelose MG…needing only a Barrel rechamber and sights adjustment. ( 8mm"S" M30):
Bullet was changed from.324" RN to .329" Spitzer- Boattail…the increase on Diameter was to accomodate the Original Barrel Rifling Grooves of .329" to .330"…
The smaller diameter RN worked on “Base Upset Obturation” to seal the Rifling on firing, but with reduced fouling and friction and pressure ( long cylindrical bearing surface; the M30 projectile was lighter ( 207grn vs 244grn), and Boattails don’t Base Upset…also the shortened bearing surface also lowered metal fouling etc.
The case was simply lengthened to allow for a heavier powder charge (lighter bullet, higher
velocity) and also for the longer reamer to cleanup any neck and throat erosion from the M93 Cartridge.
Any Barrels too eroded were replaced.
Also to note that whilst the 7,62x51, the 8x50R, and the 8x56R
All have similar Head to Shoulder Lengths, their case capacities and Head diameters are Widely Different…470" for 7,62; .488-.490" for both the 8x50R and the 8x56R.
Also, the Powders used are also different, both Chemically and Physically.