oil drain plug washers

[Maengelito]

so you know those washers that you're supposed to replace on the drain plug everytime you change your oil? i assume that its made of some sort of soft metal that expands to prevent leaks when its heated up. subaru uses these weird crush washers that have a sorta lip on them, but i was thinkin that i could just buy a handful of copper washers for a lot cheaper than the buck and change per washer for the suby crush washers. tell me why i shouldnt do this...