The bane of Indian missiles has always been "materials" - all Indian missile casing/frame etc weigh way too much!!Brains don't work on algorithm or reason. It is quite possible that Indian fuel for missiles may be of poor quality but is most likely not. India is quite advanced in technology and has been continually upgrading its technology for 40 years in missile propulsion.
Brahmos missile weighs 3tons and travels 450km. So, I would not be extrapolating too much if I say that Akash missile, which weighs 25% of Brahmos will travel at least 25% the range. I know that fuel is solid in Akash whereas it is liquid in Brahmos. Indian made propulsion for Barak-8 with dual pulse motor and weighing 280kg has range of 80km. So, Indian propulsion system is pretty good even in solid fuel rockets. I find it more convincing that 70-80km range is more warranted.
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That said, in the specific case of Akash, the operational range of the missile has also been limited by the tracking range of Rajendra radar. With the incorporation of seeker in Akash Mk1S the effective range could be slightly more (in a tail chase scenario).