In general, a two channel system has been adopted - a green channel for passengers with nothing to declare and a red channel for those with items to declare. When value of currency notes carried by the passenger is $5000 or more or when the average value of currency including US currency is $10,000 or more, the passenger has to declare the money at the customs. As a general rule, fire arms are not part of free allowance for passengers. Passengers are also generally allowed to carry a maximum of 200 cigarettes or 50 cigars or up 250 grams of tobacco and a maximum of two litres of alcohol. Gold or silver can only be carried in the form of ornaments. Trafficking in narcotic drugs like heroin, charas or cocaine is punishable by imprisonment.
It is best to check the customs website for a more detailed guide to your entitlement.
More information can be found at:
http://www.cbec.gov.in/travellers.htm