Complex sentence: The gimmick gun introduced in the second pilot was a custom-built revolver called the LeMat, based on its historically authentic counterpart; the Le Mat featured an auxiliary shotgun barrel under its primary barrel.
Split into simpler sentences: The gimmick gun introduced in the second pilot was a custom-built revolver called the LeMat, based on its historically authentic counterpart. The Le Mat featured an auxiliary shotgun barrel under its primary barrel.