Identify Anti Aircraft shell etc

I picked up what appears to be a 1" AA shell at the weekend. I believe it's 1940 date, would like to find out if I am correct in thinking it's AA and what gun it would be fired from. It has a solid boat tail ogive, much like a rifle bullet. Primer appears unstruck.
I have placed a .303 case and 75mm French case for comparison.
Also this particular 75mm case appears blown out around the central section. Could it be from being fired in a well worn breech? It does not appear to have been hammered. It is of 1918 vintage.

Attachment 93812Attachment 93811Attachment 93813Attachment 93814

Looks like about a 20mm size. What does the bullet measure, or the case mouth?

The bullet measures exactly 1 " at it's widest. Measured with a vernier caliper.

25 X 193.5 mmR French anti-tank gun ?????
Just a wag .
Chris

I'm guessing it is a 20mm oerlikon round.

The round's diameter is 1 inch, which is 25,4mm. I am assuming the 40 stamp on the base is the year of manufacture, but it's a guess.
I've not found anything on line yet with similar dimension's; so will try and expand my search.

2 possibles for the 25.4mm Rimmed ~ LM - Cartoucherie du Mans, Le Mans, France, CN - Unknown Factory, France

As for the 75mm French QF case the impact dent on the case would make it appear to be a bulged case as you can see the side walls as the pic depicts taper back in towards the just visible shoulder & case neck, I feel the case is only deformed from that damage sustained by unknown causes.

I think that Chris was correct in his earlier post. Looks like it's a 25mm Hotchkiss Anti Tank gun round. Used by French and BEF in early 1940. Not much use against the German tanks but useful against other vehicles. The case dimension is the same height and also rimmed.
Photo on Wikipedia shows BEF soldiers practising with the Hotchkiss and the round being loaded appears the similar.

I have a Japanese 25mm round that looks just like it with the exception that my case is rim less. Plus it has Japanese script on the base.