What plastic is this stock made of?PVC,NYLON,ZYTEL?etc. want to fill the forearm to stiffen it just to know is helpful.

I would check the Remington website, and it may give you a trade name like they did on the Nylon 66's (Which weren't technically "nylon" by Zytel).

This is the closest guarded secret in the world,from the evidence I have collected however it seems likely it is ABS ,nothing written on paper and signed However,no one will fess up ,least of all big green.synthetic sounds more ..uh..secretish ,tacticool,than say "pipe plastic.