As noted in the 0.49 changelog, guns should be spawning with their used ammunition, and magazine or clip. This does not appear to be working however, as it seems to still be in the hands of luck to find a rifle with its magazine or clip with it in the same building.
I request this be fixed as it has been noted in the official changelog, and for me, has been a long awaited feature as I believe that all weapons should spawn with at least 1 of their smaller magazines, such as the 10 round for .22 rifle + pistol and 20 round magazines for M4.