The original M1 was 30-06, of course, and was loaded the same way. I never heard them referred to as 'clips' but rather end-blocks. The M14 as the I think the '03, etc. has that little dove tail cut in to the receiver to accept the end of a 'stripper clip'. Once the clip is inserted, you pushed down on the rounds to fill the existing magazine. They are still available and the M16/M4/etc ammo also comes in those stripper clips and a device to reload the mags are available.
Does that match your understanding?