.500.450 No.1 Carbine query

I have a couple of questions that I hope you guys can help me with. Pictured are three different No.1 Carbine rounds. Left is Eley and right is Braendlin Cadet. My query is about the one in the middle with Eley Bros headstamp. It has a battery cup primer and it looks as if the base is seperate. Is this correct? The headstamp looks like this: Eley Bros ----- <> -------. Is that correct? Looks like a diamond shape at 6 o’ clock. Lastly, is this an older version of this caliber? Thank you in advance.

Nice, new one to me & it certainly does appear to be a Boxer type case. I’ve seen this construction on several types of British revolver rounds. I think the earliest would be those actually made by Westley Richards, WR primer & no headstamp. Probably most earliest by Eley.
couple of packets
WR No 1 Carb pkt Braennlin Armoury Cadet rifle pkt


Thank you Pete for the confirmation and the pictures of the two boxes.