Creo que mas bien se referian al alcance del combustible porque los mig-21F si llevaban cañones.
Pues en la pagina de la IAF dice que los primeros modelos no lo tenian, pero que se montaron en una góndola:
Wg. Cdr. Dilbagh Singh was the Squadron Commander and the working up of the squadron was commenced. Having a limited number of 6 aircraft for training would hardly make a contribution, but the pilots made best use of what was available. The initial MiG-21Fs had no gun, only K-13 air-to-air missiles. On the insistence of the pilots an external gun-pod was fitted. But this was limited to only the Type 74.
http://www.bharat-rakshak.com/IAF/Histo ... iG-21.html
Lo mismo ocurria con los MiG-21PF. La góndola se denominaba GP-9 y montaba el cañon GSh-23L gun de 23mm.
Saludos.