Anybody got any info on what kind of polymer usually used to make gun parts?

People usually just mention that a certain parts like buttstock, grip, and even lower receivers were made using HDPE polymer. But is there any info on what kind of polymer material was exactly used to mold those parts?

I know it's supposed to be top secret but.. Does anyone here happen to know anything?

Do companies like magpul, glock, or even FN and CZ which produces polymer receiver develop their own polymer materials instead of outsourcing them?

Most plastic parts in present day AK (stock, grip, forend) are made from plastic known as Polyamide-6

They outsource the development, from what I've read. Except Glock, since they're a plastics company, who just happen to make a great handgun.

Nylon (polyamide) 6 and 66 are almost ubiquitous in light-weight, hard duty tools and firearms. they are available with varying proportions of glass and carbon-fiber reinforcements, lubricants (molybdenum), and other additives. Mechanical properties depend heavily on both design and manufacturing choices, but a wide array of modeling tools and services are available. 

I recall working with Oerlikon on discarding sabot parts some years ago. At the time their Zurich injection-molding operation was heavily involved in optimization and production of high-velocity textile-loom parts - reinforced nylons. 

Thanks everyone, what about polymer used to make lower receivers?

I assume they need to be made stronger compared to stocks and grips to be able to withstand the force and friction of the moving parts inside it.

I know HK used to reinforce their grip assembly interior with steel.

But it looks modern polymer lowers is strong enough without any reinforcing. Like SCAR, Bren, APC, and ACR cmiiw.