The problem isn’t the overall number of shots fired. The problem is the pause between the first seven and the remaining four.
Why ?
The 'other' audio that was discussed here on FR days ago was the one where a reporter was recording the aftermath, and a 'witness' is overheard telling another gawker that the officer was 'missing' Mike Brown.
Regardless, the first 7 shots didn't all hit Brown and he apparently was still coming at the officer. A pause and then firing more rounds seems totally appropriate.
If we assume your count 7+4 is accurate, then we should find that the officer's gun had two bullets unfired. Do you think that will be the case ?
What’s the problem with the pause?
After 7 shots, one may be assessing the situation, and/or incredulous at the fact that Brown was still closing distance for attack.
The pause means Brown had a chance to stop after ample warning to. He didn’t.