Unknown Cartridge Cases. Any Ideas Anyone?thanks.

I have a collection of a few cartridge cases going back to WW1 - and sometimes I buy and sell, though not specifically. My other half is not so easy to fool these days of retirement (probably 'cos she's still working), so I've run out of hiding places.
My maternal Grandfather (a Major in the Army Service Corps), had a house full of live ammunition, luckily long gone in the so-called amnesties of the 1960's (Incl 6 Lee-Enfield 303's, stacked either side of the front door). Plus a live Verey or Very Light, highly polished, next to an open coal fire. I got into trouble aged 7, for extracting the parachute assembly and was caught trying to stuff it back in.....Oh well. Innocent days.

Could be a 3 pounder Vickers or Hotchkiss 47mm casing.
Not sure witch one as this is not really my field.
The N stands for Naval or Navy.