Our forged upper receivers are a great compliment to our forged lower receivers and are batched either with a MIL-Spec or Thermal Fit bore.

MIL-Spec inner dimension measures at 1.000 -0.0/+0.002″

Thermal Fit inner dimension measures at .997 -0.0/+0.001″ and requires the application of heat in order to provide a solid mate to the recommended barrel extension.  By heat we mean more than granny’s hair dryer.