While I would like to agree with the lar example, the antique Area of law is so much more strict in my view. I would not personally risk it. In addition, try explaining to the cops that just because it will chamber the 38 LC doesn't mean it can fire it as the barrel is slightly undersized. I bet dollars to their donuts that they say "no chance in hell, you and this gun are coming with us".
Just not something I would personally risk. Now if the cylinder wouldn't rotate or close because the rim was too thick, but the round would fit into the chamber itself, that would likely be fine. But if you could chamber and technically cause the cartridge to discharge, a no go round, safely or unsafely, I would be very hesitant on carrying that in the bush or firing it somewhere restricted cannot be fired. Just my opinion.
I want to say that, according to a distinguished and experienced member on this forum, a revolver that just so happens to chamber and fire 45LC, but was never designed or modified for it (I.e. cylinder develops enough end play over it's life that, eventually, the gun can chamber and fire the thicker rimmed 45LC ammo without problem), this is not necessarily an issue or reason to remove antique status from the gun. It was never designed nor modified for this purpose. Would I personally rely on that in court though? No chance. Crown is likely to say that you intentionally wore down a component to allow it to fire 45LC, or that it was modified just not intentionally, and that the firearm should have been repaired to allow it to remain antique.
I know I certainly wouldn't risk it, so same with the 380 thing.... If you can slip a 38 colt round into it, close and rotate the cylinder, and cause the firing pin to hit the primer, I'd suggest that you are risking bring charged on a number of points of law regarding handing, firing, owning, transporting, a restricted firearm. Will this happen for sure? No, but in this country with these convoluted laws, do you really want to risk it?
I do also realize that, according to