A gas block for AR-platform firearms is provided which is easier to install and index on a barrel of the firearm by utilizing a wedge (e.g., collet) system. The body of the gas block may therefore be relatively precisely circular, allowing for easy movement into position on the barrel of the firearm. The gas block is stronger, tighter, more durable, and more reliably stays in place than prior art gas blocks. In one embodiment, the gas block eliminates forward gas leakage from between the gas block and barrel. The gas block is interchangeable with standard prior art gas blocks commonly found on barrels of existing AR-platform firearms. The gas block is also compatible with low profile and MLOK handguards for AR-platform firearms.