25 yard yard quartering away shot is not a bad shot to take in my book. If you got penetration half way down the shaft, you should have had enough penetration. It sounds like you may have hit some heavy bone however. If you didn't see any bubles in the blood and the blood was not pinkish, you propably did not get a lung. If it was bright red, then it was proabably a muscle hit which probably will not be fatal. My guess is that you hit too far forward on the deer.