Centurion Arms Tabbed Gas Block
Most of the AR-15 barrels from Centurion Arms now come with a notch that is milled TDC in the shoulder of the gas block journal. This notch aligns with the gas port of the barrel and is intended to interface with the Centurion Arms low-profile “tabbed” gas block.
A precisely machined “tab” on the Centurion Arms gas block dovetails with the notch in the shoulder of the gas block journal to align the gas block with the gas port of the barrel. You can still use a standard 0.750” low profile gas block (or an A2 front sight base) with the Centurion Arms barrels, but you won’t want to, as the tabbed gas block is a work of art.
The notch in the shoulder of the gas block journal has a nominal width of 0.1020” as measured with Mitutoyo digital calipers. The tab on the gas block has a nominal width of 0.1014” as measured with a Mitutoyo micrometer. This creates a transition fit with a clearance of only 0.0006” and there is no rational play with the gas block mounted on the barrel.
With the tabbed gas block pressed against the shoulder of the gas block journal of the barrel the set-screw threads of the gas block are precisely aligned with the dimples in the 6 o’clock position of the Centurion Arms barrel.
The Centurion Arms tabbed gas block system makes the process of precisely aligning the gas block with the gas port of the barrel practically foolproof.
The Centurion Arms 0.750” low-profile tabbed gas block weighs 1.1 ounces. As mentioned above, the version that I reviewed is drilled and tapped for use with two set-screws to secure the gas block to the barrel. The US Army Marksmanship Unit discovered years ago that pinning the gas block to the barrel can degrade accuracy.
The bore of the tabbed gas block has a gauged diameter of 0.7495”. When mated with the Centurion Arms barrel that has a nominal gas block journal diameter of 0.7493”, these components have a tight transition fit with only 0.0002” of clearance.
The gas tube channel of the tabbed gas block has a gauged diameter of 0.1801” and when paired with a Centurion Arms mid-length gas tube that has a diameter of 0.1797” at the proximal end, these components create yet another snug transition fit with only 0.0004” of clearance. These tightly toleranced components all contribute to a very efficient gas system and it’s quite refreshing to see a company that produces AR-15 components that hasn’t let their quality control deteriorate over the last few years.
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