Gujarat High Court Criminal Manual (subordinate court practice), 1977
If an application is made for the summoning a fire arm expert in a case, the Magistrate should first ascertain from the party wishing to call him as a witness on what points his evidence is required and then write a letter to the Expert asking him if he is able to give evidence on those points and whether he wishes to examine any exhibits before giving an opinion. After these preliminaries, if the reply of the expert shows that he is in a position to give relevant evidence, then and not till then, summons should be issued to him to appear as a witness.