I think Daryl has recounted the real world terminal performance (or lack there of) of these things on large game- based on actual animals and trusted accounts of the circumstances leading to thier wounding. Bottom line is it is just not worth messing with at best and down right unethical at worst. If you want more umphf barrels are dirt cheap and they come in lots of sizes.
Keep it simple- Put a round ball on the hide covering the lung, wait a bit and then go get to work.