Gunsmithing White filler in stocks?

Ackley Improved

Sergeant
Full Member
Minuteman
Oct 31, 2006
283
37
AUSTRALIA
I am after what the substance is that guys like McMillan use inside the stock as the filler. Some sort of high density foam that sets pretty hard.

Going to try to make a stock for myself... only for the fun factor, so time etc no problem.

Whats the worst thing that could happen? A bloke with to mould half stuck together and cant get the dodgy made stock out...

Fun times!!!

Cheers