I have killed a few deer with 00 buckshot. The deer were being pushed by dogs in the Tidewater area of Virginia. It does the job very well at reasonable ranges but you still must place the shot correctly in the neck or chest for it to be effective. Even 00 buck does not penetrate well from a bad angle, and the smaller sizes are much worse.
Deer hunting in that area is a social occasion with very large hunting parties and lots of dogs to run the deer for them. Some of the guys hunting with me blasted away at every deer that was pushed by them hoping the dogs would find the deer for them. This plan did not appear to work very well. Almost all of the local guys used #4 Buck ("in case I see a turkey"). It was sad to think of how many deer those guys hit but did not recover. However, those guys also brought a lot of deer out of the woods if they hit them well.