I don't think it has much to do with how many rounds you shoot. It could be the first one or the 10th. But if on one of your shots you aren't holding her down correctly she will bite you and it will make you flinch. I always bring the .22 to the range for just this reason. 30 rounds of .30-06 isn't all that bad at all. I agree with others that sound can also make you do it.

I hate the flinch. I always feel disappointed in myself when I get one.

Tom