Plastic scares me... Here is why. All plastic things I have ever known of eventually get brittle and crack or break... If plastic gets hot it gets soft, then melts.
If it gets extremely cold, it cracks, and breaks. Certain chemicals, like oils, get on it it cracks, breaks and melts... Sunlight decomposes it, and it cracks and breaks...
A flintlock from 1776, if it recieves even average care will still work today... Even the aluminium M16 will last for thousands and thousands of rounds.

In 1982 I was issued an original full auto AR15, made around 1963. I used that rifle for several years and then my partner used it for several more years. It shot many thousands of rounds, we replaced the barrel as needed. I retired in 2006 and it was still going strong.

I just do not trust "Plastic"...