The Holland & Holland Chain shot was designed to tear through the rigging of aircraft and would have been largely ineffective against Airships. For this purpose, Buckingham had designed a .707 (12b) incendiary round to be fired from the same weapon as the chain shot. They also used Martini carbines and the Royal Laboratory “Flaming Bullet” in .577/450 calibre.These were used by the RNAS rather than the RFC, and were obsolete by 1916.
When Leefe-Robinson brought down the Shutte-Lanz SL11 (actually not a Zeppelin) in September 1916 he was flying a BE2c armed with a Lewis gun firing a drum loaded with alternate Brock and Pomeroy rounds.
The “boffins” you speak of would have been from Royal Laboratory, Woolwich, where people like Threlfall, Hardcastle, Todhunter, Jones et al were trying to develop effective explosive incendiary rounds for the .303 and later .5.
I agree that many books are vague on the subject of .303 special purpose rounds, and there are a confusion of types. Eventually research was concentrated on making an explosive bullet stable enough to be bore safe in a machine gun, yet sensitive enough to explode against aircraft or airship fabric. An added complication was that a slight delay was required to that the round penetrated before detonating. There was no airburst type.
The most successful type to actually enter service was the RTS, and there are even two or possibly three types of this round. RTS stands for Richard Threlfall and Son. Work was continuing on these and other types when the war ended.
Forgive me if I do not post too much more information at this point, as my putative Ph.D thesis is on the development of British special purpose ammunition in WWI, and the thesis is supposed to contain unpublished research!