Acting on a tip-off, STF arrested Firoz Abdul Razzaq, Bahadur Singh, Kashiram and Kushal, police said.
While Firoz belongs to Rajasthan, the three others are from Madhya Pradesh's Barwani district.
According to STF sources, Firoz arrived here for purchasing a pistol to allegedly eliminate a Rajasthan-based contractor but was arrested.
Later, STF sleuths also arrested three other miscreants involved in the sale/purchase of illegal weapons, they added.