Six birds is cutting it kinda close if you are just using a 20ga. I can see it being successful if you used a .22 starters pistol first. I also took my dog to a game farm but used a .410 but before that I also took her to empty fields alot, including the area where she would be hunting and used a starters pistol at every bird she chased.

Also, 50 yards is common for pointing breeds. When your dog gets comfortable and can see you then they will range further out. At 10 months, your dog is going to stick relatively close.