Multiball loads were used by militaries during the BP days for military police purposes; riot control, etc and were commonly known in the USA as guard cartridges.

Speaking of barrel ringing. Make sure your load is "trail proof", meaning, rough handling will not allow space to develop between the RB's in the case. Always remember that what is workable at the range may fail or even become dangerous if kept in a gunbelt or pocket or pickup jockey box over time and subjected to knocks, vibrations, etc. A load that allows significant space to develop between the bullets can create "barrel obstruction"-type damage to the gun if one pellet sits right on the powder and the other pellet {-s} are a ways farther toward the mouth of the case and there is space between them.

Ditto if you have a poor crimp and the front bullet rolls into the lands and the other two are fired behind it.