Picher, a barrel whips, wiggles, vibrates shimmies or whatever at the same frequency for every shot. Mild loads make the amplitude smaller than heavy loads. Why? The barrel's shape and metalurgy remains constant so it has the same resonant/fundamental frequency and the same harmonic multiples. Same as a key struck on a piano causing a hammer to smack the middle A wire string. How hard determines whether the sound is loud or soft, but the note stays the same; 440 Hz.
Therefore, the only thing one can change is the bullet's barrel time from case mouth to out the muzzle and the amount the barrel wiggles not its frequency. Check this site's page out:
http://www.varmintal.com/amode.htm
The one below explains how the BOSS works; it ain't like Browning says:
http://www.varmintal.com/apres.htm