Never heard of such. The designation rather makes me think of a slow, non continuous-tone film. What was it used for in 16mm?
Though "shellburst" then makes me think of film used in high-speed photography for materials testing (where in the lab sufficient lighting would be).
I just saw some for sale. First time I'd heard of it too. I think it was iso250 and was used to film missile / bomb explosions. Seller had some nice continuous tone shots using low contrast developers with it but thats all i know
I shot this film many years ago in the sixties. I worked at camera stores in LA that catered to JPL and the aerospace industry. IMHO it is a selective sensitivity film mostly used for aerial or missle launch photos. It was useful in analysis of fine detail in mostly sky filled scenes. Aerial films are often low contrast. If I remember correctly it was around 320 ISO and generally reproduced flat images. I think using a dark red filter might also be used to darken skies. I used it for low contrast portraits.