Is it uncommon for a groom to hear his best man’s speech before his wedding?

I don’t think that’s customary. mostly because the best man usually doesn’t finish the speech until minutes before the reception! I went to a wedding 2 years ago where the best man literally made up the speech on the spot, he wrote nothing down in advance. my husband’s brother did write his speech a few days before our wedding but we wanted it to be a surprise, it never occured to me to ask him to tell us what he would say in advance. I think that’s pretty rude, because it doesn’t show much confidence in your ability. if you prefer to keep it a secret, either tell the groom you will show the speech to your Dad for him to approve, but it’s best if the groom hears it for the first time at the reception.