|Your manager's behavior is not surprising since people tend to see their own shortcomings in others. Since he is a classical blamer, he is likely to see the same trait in others, whether it exists or not. The reason he is quick to spot this negative characteristic in others is that he is so familiar with it in himself. |
At this point, although you can give him more information regarding your troubled project, you are not likely to change his mind. In fact, he is likely to interpret your follow-up communication as further examples of blaming by you.
You need to recognize that this is one of his character traits, and the best you can do is to try to prevent it from appearing. In the future, if a project is not going well, do not wait until you need an extension. Go to him at the first sign of trouble and ask for his help. Stay away from explaining why your project may be having problems, and focus specifically on the steps you would like him to take. He may still go into his blaming mode, but at least the project will have a chance of being saved.
In the meantime, no one would blame you for looking around for a better opportunity, or at least a better manager.