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I haven't spent much time with the dog it could be that it isn't cut out for hunting at all. Just wouldn't want to write it off just because of size
Size absolutely matters, but build matters more. Short legged dogs will never have the stamina and ground covering ability as long legged dogs. With that said, I just got done hunting over a springer build almost exactly like the dog you describe. He couldn't cover the ground as fast, and didn't have the stamina of the longer legged springers we hunted over, but he could track birds as well as any of them, and he put lots of birds in the air. Has your buddy put his springer on birds? If the dog ignores birds, your buddy has a house dog. If the dog goes crazy over birds, he has a bird dog.
Just to add, the "show type" Springers are tall and long legged; I own one with some show champions in his lineage. The field type Springers are generally smaller, more compact, with shorter ears, less hair and yes, somewhat short of leg in some strains: http://englishspringers.weebly.com/field-vs-bench-bred.htmlYour friend needs to get a good book like "Training Spaniels & Retrievers" by Ken Roebuck and TAKE HIS TIME in introducing the dog to especially gunfire. Tossing a wing for the dog will reveal if the dog has any interest in becoming a hunter. I just hope he does not take the dog out on a first hunt "Platoon Assault" upland hunt with all the Buds to become gun-shy and useless as a hunting dog.Tom