I've tried the can test often, and I can say it's not very reliable. I had started to try to do a chrony vs can test to try to revise the Redwolf numbers for cans used here in Canada, but results were too inconsistent. I found that in some cases, a gun would shoot right through both sides of one can, and barely make it through the side of another. It's really not reliable.
My CA M15 currently shoots 385 fps, and can easily punch through the centre of the bottom of any can. My JG 416 currently shoots 425 and can easily punch through the edge of the top of some cans, but not others.
So while it's a fun test, it's not very reliable.