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  • Post last modified:October 12, 2023

The gas block is under the handguard of an AR-15. It's over a hole on the top of the barrel. When you shoot, some gas goes into this block and then back to the chamber. Some AR-15s have too much gas going back, which can make the gun dirty.

How to Pick the Right Gas Block Size for Your AR-15

ar15 gas block

Referenced Strike Industries

To get a new gas block, you need to know its size. Online, you'll see a size like 0.750". This size should match your barrel's width.

Most AR-15s have a 0.750" barrel. If your barrel is thin like the old M16A1 design, you need a 0.625" gas block. Thick barrels need a 0.936" gas block.

If you're unsure about your barrel size, you can measure it. Use calipers from a store to measure the barrel near the old gas block. Then, you can buy the right gas block.

Other Things to Think About When Getting a Gas Block

ar15 gas system length
  • Adjustable Gas Blocks: These let you change the gas amount when you use different bullets. This can make your gun parts last longer.

  • Low Profile Gas Blocks: If you have a special rail system for better aim, you might want this type of block.

  • Lightweight Gas Blocks: If you're in gun contests, think about the weight of your parts. Lighter blocks add less weight to the gun.