There WAS a specific magazine made for the Carbine, but the majority of them got switched-out during post-War FTRs.
Thing is, the Carbine was properly a Number 5 and was based on a lightened Number 4 action, which the Armourers had in plenty. Remember, the Number 4 magazine was MACHINE-MADE and far cheaper to produce than the hand-made and hand-fitted Number 1 magazines. Result was that Number 4 and 5 mags were cheap enough that they could be replaced rather than futzing with them if there were a problem. So lots of Carbines ended up with Number 4 magazines; according to the later manuals, they were the same magazine!
A Number 1 Magazine can be persuaded to function..... sometimes. Better just to use the right part.