Why doesn't Cav Arms (or someone else) produce polymer lowers which look like the average aluminum lower (i.e. designed so you can add your own pistol grip and buttstock)?  I would consider a polymer lower, but I don't want a fixed buttstock and I don't particularly like their pistol grip design.   Very curious on this ...

Vulcan/Hesse does.  Buyer beware, though.  Many have had good luck and some have had grossly out of spec lowers from them.  The main problem is that they don't take returns or offer refunds or exchanges.  If you get something out of spec from Vulcan (or their big distributor JoeKen), you are SOL.  Buy at your own risk.

I believe in large part it is due to the nature of the material being used.  Polymer material is more flexible than aluminum, and to keep the dimentions to that of original AR15 lowers would require a stiffer and more expensive material.  To use a pistol grip with an attatchment screw assembly would likewise require a stiffer material than polymer.  Such as the carbon-fiber used in the guns that Bushy is making.  

Different materials require a different approach.

Tex78

Oops, forgot aboout that Bushmaster is making the Carbon-15s now.