The Old old CFC Antique Letters used to list the caliber.
Not anymore.
But you can call them and ask they will tell you 45 ACP webley is AOK they will letter it knowing its converted to 45 ACP.
and there the RCMP now not just CFC

Years ago i used to ask the caliber be put on my letters.
But they dont care anymore so neither do i.
Its very confuseing this Antique caliber thing.
Like this a 1889 WG army that was made before 1898 thats chambered in 455/476 now most can and do chamber and fire a 45 Long colt. there not ALTERED to fit the 45 colt it just happens to fit.. Now you would think well thats not a perscribed antique but it is.
Why because the WG was never factory chambered in 45 long colt but just because it happens to fit that dont matter.
Again explaining this to a CO or Cop in the feild would be intresting to say the least, id prefer to not have that conversation. LOL
But 45 ACP is AOK and so is any caliber not on the list.
But you cant say a gun is now chambered for the 357 magnum because the 38 Sp fits perfect into the 357 chamber. 38 special is on the list but 357 is not.
So its very confuseing i can understand a person being carefull if there even abit worried about ending up in court.
Look at what RCMP / CFC says about the 38 M&H now.... thats something the RCMP Just decided to say no more 38 cal M&H will be lettered Antique because its to close to 38 S&W.