Well, first who is asked to produce this round ball? THEY have to prove he was in violation; he doesn't have to prove he was in compliance. In court you can't ask the defendant to produce evidence against himself.
Second, how does the defendant know the ball is actually .395... the label on the box or did he measure it? He probably doesn't "know".
Finally, he was cited for hunting with a bullet smaller than .40 caliber. If they didn't pull and keep the round ball from the rifle, they don't know either... they assume.
The questions to ask the officer are,
"If you came across a hunter using a rifle, and he shows you a round ball and tells you it's .440, how do you know he doesn't have a sabot loaded in the rifle with a .358 bullet? So the only real way to know would be to pull the bullet and measure it, right? How would you know the ball he showed you was .440 and it was a .45 rifle? How can you tell it's not a .395 ball and a .40 caliber rifle which he claimed was a .45? Do you ever measure or do you simply quiz people? If you do measure did you do so, and if not why not? What would you have done if the defendant had said he had a .45 and it used a .440 ball? Would you simply walk away? So you just take a person's word, but you don't really know if the person was incorrect about the bullet size? When a person is speeding does an officer use a measuring device, or do they stop the person, and ask them how fast they were going, and right them the ticket based on that? So you come across a driver who when stopped says they're drunk... you don't do any field sobriety tests or offer a breathalyzer, you just charge them? So back to the defendant..., you don't have any real evidence except for an alleged conversation?"
Again, it would've been simple for them to impound the rifle and have the ball pulled with CO2 and measured, and so you'd simply pay the fine, as there would be no argument. That's what I would have done, and I'd have already photographed the rifle for court and given it back to the defendant to boot.
Yep you screwed up but that doesn't mean the LEO's get to be sloppy about the job. As an LEO of 23 years, that was a sloppy job (imho) and you demonstrated good faith by not lying to them on the scene.
LD