The present investigation arises from the need to investigate and experiment scientifically if the contaminants established as controlled and uncontrolled variables can affect the performance of the procedure described in numeral 4.1 of the guide 2DCGU-0024 "to perform ballistic procedures to the weapons (firearms, pneumatic, gas, phisto, detonators, electric, among others) and entry to the ballistic identification systems"; it can be reasonably inferred that when performing the forty-two tests, manipulating solutions A and B of the Griess reagent, it is evident that the contaminating agents transferred to the interior of the barrel (4-stroke oil, diesel and gasoline) do not affect the results for the identification of nitrites product of the combustion during the firing phenomenon. The opposite case occurs with rain water, since it is observed that it affects the elaboration of the test, taking into account that without coming into contact with the deflagrated gunpowder, it gives as a result a faint pink coloration, which indicates in a preliminary way that it is positive for the presence of nitrites.