It might not help the opening poster but I got two .270 slots so that I could buy a new rifle without having to sell my existing rifle before acquiring the new one. This was with North Wales Police who, at the time and contrary to previous experience, had a sensible and pragmatic FLO. He also gave me “Any Legal Quarry” on all my rifles when I complained that if I was out with the .270 I couldn’t shoot a fox if asked to by the gamekeeper because the rifle was conditioned for just deer, boar and zeroing.
I often think it would be a good idea if, instead of for a specific calibre, slots were granted for a generic calibre, so for a .300 slot you could have any calibre that qualified e.g. .30-06, .270, .308, .275 or 7mm and this would mean that you could change from say .270 to .30-06 without having to worry about getting a variation and of course having two slots for a generic calibre would allow a choice and daytime/nighttime set ups. Two generic calibre slots would cover most people’s needs covering calibres from .22-250 to .308. Even better if FACs were credit card sized with all the information on the magnetic strip and Firearms Dealers had readers connected to a central database that could add new weapons and deduct weapons traded in thereby automatically opening up the slot. I know! Far too sensible, it will never happen!