If your barrel isn’t marked, how can you tell what twist it has? Simple, get a cleaning rod with a swiveling handle. Fit a tight-fitting patch in it, and stuff the rod with patch down the bore. Make sure the patch can go both directions. Push in until it is ore than halfway down. Wrap a piece of masking around the rod, with the ends stuck together, forming a “flag”. Attach this flag with the ends straight up, as close to the flash hider as you can. Then slowly pull the rod out, watching the flag rotate. When it comes back up to vertical, stop. Measure the distance from the flash hider to where the flag is now. That’s your twist rate.
To read other ‘smithing tips and techniques, purchase Gunsmithing the AR-15 from Gun Tests.
