The majority of the hull components are aluminum. Various components for the suspensions/ running gear and transmissions are steel; some carbon, some stainless yet others hardened steel. Significant brass is used in some outer accessories.
To give you an idea the power that these 'toys' will generate the
final drive shaft to the sprockets can be as large as .375" ( 3/8") steel and if you aren't diligent you can easily bend them. In first gear some of my models if they can get traction, can pull a disproportionate weight many times their own.
I must add that I did not build the SU-152; it was built by a fellow in the Ukraine. There were 2 made. There's a video of a local event there and they had fit a .410 blank gun the the example they ran. See it here:
http://www.youtube.com/watch?v=O9L3I...8%3Btopicseen&
(They didn't have the main fighting compartment fastened down and watch it jump!!)
I have electrically driven ( 6 shot) 8mm theatrical blank guns for some of mine but I do not fit them. Our society , especially here in the People's Republic of California is too much against that sort of thing to risk getting in dutch over it.
Jerry