I'm not sure what you mean by "not good quality" ?
Has it been fluxed well to remove impurities ?
Do you know what the composition of the alloy is ?
do you have a hardness tester to test it if you have a mystery alloy,
so you can get a fairly accurate idea of what it actually is ?
when you know what the alloy is, you can see on this link
(for future use, it's at the bottom of the page)
what Pressure that alloy (as a plain base boolit) will handle.
http://www.lasc.us/CastBulletNotes.htm
most reloading manuals will give you a PSI pressure rating of a Max load,
you can then guesstimate what your desired load will generate,
ideally less than you alloy will handle.
With all this said, BAC lube will probably work,
but once I get above 1200 FPS,
I generally move to a higher speed Lube like Carnuba Red.
in conclusion, I understand that a lube will not overcome the
problems that an alloy that is "not good quality" will create.
Jon