Reynolds, a lot of "match" actions have a cutout for a box magazines; Win. 70, Rem 40X, M1903, and others. Some have a clip guide put on (or milled into) the receiver bridge so 5-round stripper clips can be used to reload in rapid fire matches. The Win. 70 sporter box magazine actions have shot groups just as good as those custom ones without the magazine cutout. But Winchester made a couple dozen magnum length ones without the magazine cutout (totally solid bottom except for the ejector slot) for the US Army Rifle Teams in the 1950's and were chambered for the .300 H&H Magnum.
In the beginning, when it all got started, magazines had a spring to push rounds up to their loading position at their top. Clips never had a spring to push rounds out of the to a load position. Paul Mauser's clip design used a flat spring to press the rounds against the inner ridge so they wouldn't fall out in handling. Springfield Armory got rights from Mauser to use the same design for the M1903's.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master