I wouldn't count of a little piece of paper for that.
Has anybody been caught in the bush and shown a letter to the police?
Yes, I have. The officer was polite but concerned when I showed him the antique status declaration. He was with a Conservation Officer that had been told about a crazy man running around the bush with a revolver in a holster. He felt he should have some backup so asked a Constable to attend with him.
They were polite and ASKED me if they could hold the firearm in their vehicle while they contacted someone that could clarify the issue of their concerns to their satisfaction.
It took about 10 minutes of being transferred from his head office to somewhere else. The Constable came back to me and handed me the pistol. He had a friendly way about him and they both apologised for the bother.
I offered them a coffee and it soon became apparent that they both wanted to try the pistol out on a target. They both shot off six rounds and were impressed by the recoil and accuracy.
Then of course, I was asked how the pistol performed on game. I was a bit POed at that lame attempt to catch me breaking the law and informed both of them that it was illegal for me to hunt with the pistol but it wasn't illegal for me to carry and shoot it in the field, as long as I was doing so in a safe manner and not irritating the neighbors. I also told them the pistol was unloaded while it wasn't in use and that I wouldn't leave it unattended in camp, while I was hunting.
They were OK with that. Smiled apologised for the lame attempt, got into their vehicle and left. I never saw either of them again.
One thing to keep in mind, in such situations, you may not be breaking the law but you are doing something highly unusual and to some minds controversial. Be polite but be firm and request they get in touch with someone that knows the issues involved. They can get in touch with people in the know, just about anywhere and anytime.
Keep it on an even keel and all will go well. Don't say anything you don't need to say. There isn't really a good reason for them to confiscate the pistol or charge you. Especially if you have given them proper documentation.
The letter in the link is a direct copy from the CFC website. They can check it out in a few minutes. If the situation starts going south, clam up and wait until you get to the station, then if it still remains ugly because of personal emotions, either lodge a complaint with the Watch Commander, lawyer up and lodge a complaint with the Police Commissioner. Likely, the situation will never get to this point. Possible but doubtful.