You have to use and treat huntin situations as training opportunities. You can't worry about shooting, in fact I wouldn't shoot at all until this is fixed. You have to worry about the dog and his obedience. Let your buddies shoot and you worry about the dog. It's not that you haven't taught him, it's the situation that makin him not think straight.

X2
I have done this before. Put me and the dog about 15' away from the blind, and I put him on his stand.
I put my gun up and just worked the dog. It will work, but you have to be consistent, just like any training.

Also you might try some non retrieves. meaning you/helper throw dummies and don't let the dog retrieve make him steady. have a you, a helper, or someone else go get the dummy. add in blank pistol and maybe popping up and shooting blank pistol.
when doing this only let him retrieve 25% of thrown/launched dummies.
steadiness should improve with this drill just takes time

the theory here is that you dog is pumped and knows he is about to get to go get something b/c thats how you've trained him.
Launch dummy he retrieves it.
this teaches him just because there's action on your part does not mean he gets to do anything but sit there and be a good dog

Also you might try some non retrieves. meaning you/helper throw dummies and don't let the dog retrieve make him steady. have a you, a helper, or someone else go get the dummy. add in blank pistol and maybe popping up and shooting blank pistol.
when doing this only let him retrieve 25% of thrown/launched dummies.
steadiness should improve with this drill just takes time

the theory here is that you dog is pumped and knows he is about to get to go get something b/c thats how you've trained him.
Launch dummy he retrieves it.
this teaches him just because there's action on your part does not mean he gets to do anything but sit there and be a good dog