What is it, you say? Well, it is simpler than you might think. 

This 37mm projectile only requires a 37mm aluminum casing, powder bushing , pushing disc, and stars from our star cluster kit.  To make this round, simply prime a casing with a primer and bushing just like you would with any other type of round.  Pour in your lifting charge of about 65 grains of FFFG black powder or synthetic black powder.  Put in a small amount of colored stars from the star cluster kit and cap the casing with the 37mm pushing disc.  Lastly seal the top edges of the pushing disc to the casing and kablam! You have a star cannon round for your 37mm launcher.

This projectile will shoot bright stars directly out the barrel of the launcher producing a fountain like effect.  Think roman candle but a lot of them all at once.  I typically use the small aluminum casing for this type of 37mm round.