Indexed adjustable gas block system

An adjustable gas block system for a semi-automatic firearm comprising:

• a) a gas block configured to be attached to a firearm barrel having a gas port comprising:
• 1) an entry gas port configured to allow gas to enter the gas block from the firearm barrel gas port,
• 2) an exit gas port configured to allow gas to exit the gas block,
• 3) an obstruction cavity disposed between the entry gas port and the exit gas port fluidly connected to both the entry gas port and exit gas port;
• b) an adjustment screw comprising:
• 1) threads configured to cooperatively interact with threads in the gas block,
• 2) a gas restricting portion wherein movement of the adjustment screw within the gas block alters the volume of obstruction cavity open to the passage of gas from the entry port to the exit port, and
• 3) an indexing portion;
• and
• c) an adjustment lever configured to be attached to the adjustment screw in a plurality of orientations.