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Open Full ToolMost AR15 and AR10 barrels have a thread length of 0.625". Many AR9 barrels have a thread length of 0.400". Some barrels may be longer or shorter, and you should measure your barrel to get the most accurate results.
Not all barrels are the exact listed length. For example, some 10.3" barrels are actually 10.25" long.
Many handguards are not the exact listed length. Aero in particular is really bad about this.
Listed vs actual lengths of Aero handguards:
7.3" → 7.25"
9.3" → 9.22"
10.3" → 10.25"
12.7" → 12.63"
15" → 14.94"
A thick shim or Accuwasher can be used to move the muzzle device and adapter away from the handguard and gain more clearance.
Gap (adapter to handguard end): —
There may be a small amount of variation from the theoretical value based on exact part fitment and manufacturing tolerances.
Blast baffle clearance: —
It's recommended to have at least 0.10″ of clearance to the blast baffle, but more is always better, especially with shorter barrels, heavier firing schedules, or titanium suppressors.
Total length added to barrel end: