Rapid mortar fire video

[Slick]

Shows assorted and varied rounds and activities. Glad I was never on the receiving end.

https://www.youtube.com/watch?v=G3_T1z1GpOM

 

[sksvlad]

What do those 4 yellow rings do?

 

[Slick]

Charges. Filled with some kind of black powder/gunpowder/something or other.

". . . incremental propellant charges, sometimes known as augmenting, auxiliary, or supplemental charges, can generally be fitted to a mortar projectile."

 

[Eggburt1969]

What do those 4 yellow rings do?

As mentioned by Slick, they are what I'd call augmenting charges, but in US military terminology they are now called 'Propelling Charges'.

If you are on about the bombs in the video frame grab below, then they are likely M235 propelling charges. This as the 60 mm HE bombs would seem to mostly be the M768 model (see later comment).



The horseshoe-shaped M235 propellant charges are arranged around the M27 multi-perforated tail boom in which the M702 (if the bombs are M768) primary charge (US = 'Ignition Cartridge') is placed. The M235 propellant charges hold a single-base ball propellant.

The M702 is small propellant charge assembly screwed into the rear of the tail boom that holds a percussion primer and M9 double-base flake propellant.

What's weird with these 'M768' is that they are Composition B (Comp B, RDX/TNT) filled? The M768 and M768A1 are supposed to be filled with insensitive munitions (IM) compliant high explosives, not Comp B?