The notch in the receiver your referring to was noted as the magazine cut. It appeared on all 721,722, and 700 rifles until 1966. Usefulness with stripper clips is questionable as the different calibres sometimes had a magazine spacer in the rear to accommodate shorter rounds. Although the 300 Savage may have been examined as a 30 calibre military cartridge, it has nothing to do with Remington chambering it it their 722 line in '48 phasing it out in '56. The 222 Remington Magnum did however come about due to the military asking companys to submit their rounds for a future small calibre testing. Test ammo was contracted from Remington but the specific dimensions didn't fly and Remington asked to legitimize the round after which they introduced it in the 722 line-up in '58. Remington 720s were deployed as military rifles in WW2 but in a very limited run and in 30-06 only. This is what I believe you are refering to as the military project.
