6.5 Grendel PTG Reamer

[Shivesy]

I don't really know if this has any bearing on the subject but I am curious so I'll ask. Again back tracking to a few months ago and the short chamber issues with my McGowen barrel. I made a call to PTG and talked with Dave about my specific problem. Dave was aware of the problem and stated that the Grendel was a double throated reamer. Dave also said to use a .264 LBC reamer and that reamer works just fine and much better with the Hornady Grendel ammo because this reamer uses a parallel throat. What's the difference between a double throated reamer v/s a parallel throated reamer?