Frame melting point laws...
Including a section of the GCA 68 were created and passed long before polymer frame pistols hit the market. They were one of the criteria used to prohibit the import (and in some jurisdictions) the sale of "Saturday Night Specials", which were defined as cheaply made handguns, made with inferior materials.
That was the public line. In reality, they were passed as a combination of trade protectionism, and gun control, the stated intent was to prohibit and restict the availablity of cheap handguns to criminals. The real world result was the restiction of affordable handguns to poor people, and the criminal class often obtaining a better grade of firearm.
Arbitrary size criteria, so called "sporting purpose" requirements, frame melting point limits, drop safety tests, and some other things were all passed in various localities, state and Federal laws.
Before the media and the anti gun movement discovered the "evil" of "assault weapons" (their terminology, and incorrect to boot) the main thrust of gun control was against handguns, particularly smaller, cheaper ones, under the banner of "Saturday Night Specials". They don't much go after these guns anymore, due to the successes of their campiagns against "assault weapons", and the proven documented fact that the term "Saturday Night Special" has racist origins.
Most of the laws have loopholes in them, that while prohibiting importation, the do not prohibit domesic manufacture of these kinds of arms, only restricting sale of US made ones in certain areas.
Due to the language used, some guns with alloy grip frames are banned in some places, even though they may not be the cheap junk guns the law was created to prohibit.
