Wolfe-
If I may ask what you shot the bear with. I count 400yrds or even 300yrds as too long a shot on a bear, especially a large one. I can understand +/- 50yrd error, but 100-150yrd error is allot. I hope that you do invest in a range finder, I go out some times to eyeball distances and then range to find out how close I am to the right distance. It has been one of the best things I have done to practice and train my eyes. It is unfortunate that this happened, but it is even more unfortunate that these things do happen.
Good luck, Qaz