And also, let the parts break-in, if you're building from scratch....
It took almost 4 months for my body + bolt + other internals to break-in, (ie cycle smooooothly.... :P)
(just let it sit, fully assembled ofr a while...lol)
EDIT: this I what I bought,
G&P reinforced assemble set And AFAIK they are all steel, not aluminium....
Also, I would recommend getting a G&P outer barrel + G&P hopup rubber, (5ku and ratech didnt work well....5ku barrel wasnt straight... it was curving up.....:S)
EDIT of EDIT: o wait, they ARE aluminium.... lol.... except for the main parts, like the Hammer, Full auto sear, mag catch, selector are steel....and some other pieces.... cant remember...lol
And they are solid, dont worry :P