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rightisright wrote:Moral of the story: Stay away from polymer AR lowers.
+1 I engineer polymer versions of metal parts all the time. It can be done (heck - I'm sure I could for an AR lower) but it requires a fair amount of work to get it right. All of the ones that I have looked at do not compensate for the difference in material properties nor for the fact that you will get a weld line (weak spot where two flow fronts come together during molding) at several critical locations.
All of this can be compensated for and you can actually get a more robust part if you do it right, but it takes time, work, expertise and a lot of capital to make the kind of tool that is truly needed.
The first big hint that it was done wrong is if the plastic part looks the same as the AL one.
MOST of the polymer crap out there today is just a pouring into a mold of the piece to be replicated, with no consideration to any kind of "engineering".
