I happen to know the exact shop that manufactures all of Hesse Arms AR receivers.  The aluminum and the "carbon fiber" models.  First revolation,  the Hesse prints are not derived from military drawings like everbody elses.  You can rarely change uppers with lowers within the Hesse line.  Almost impossible to interchange parts with a nother AR manufacturer.  Also, there is no Carbon Fibers in the plastic receivers.  It just plain old Ryton R4.  Good plastic for electronics, not for guns that generate lots of heat.  In 2001 when the demand for more AR's skyrocketed, Hesse got a break.  DPMS brought their receiver blanks to the same MN, shop that Hesse had been using for years.  The DPMS boys brought proper prints with all of the tollerancing and the proper government stamps.  That information magically washed onto the Hesse prints and greatly improved their product.  Not legal, not ethical and not totally successful.  Some of the Hesse parts were so far off the mark, the machinist couldn't bring them into spec because there wasn't material to do it with.  You can't weld plastic receivers after they come out of the mold.  I saw hundreds of them, tried to fit some parts and was told they all went back to tool and die guys to work some magic in order for them to fit together.  Hesse tried to reverse engineer an AR when the government would have gladly given him the drawings he needed.  Not too bright.  Really not too bright if you are buying the dam things, especially the plastic ones.  Bad Karma.

Pretty common knowledge in these parts that Hesse is crap...

I just remember someone here wanting to trade a Hesse product for something "exotic." To which someone else replied... "does a "J" shaped turd from a Mexican count?"   I still laugh about that one.

Don't worry about all those extra receivers they had laying around. This highly reputable company [rollseyes] bought them all. The company is VULCAN ARMS.

Yup, those Hesse products have gained quite the reputation around here.
The only thing their good for is as a bad example.