difference between French 1939 5 Francs KM888 and KM888a? [решено]

Is there a visual difference between KM888 and KM888a? One is nickel and one is aluminum bronze, but is there another way to verify my guess? They are both the same weight and diameter and look like they have the same design. There is a .2mm difference in the thickness, but it is very hard to see something that small.
Thanks!

The only doubt you could have it for 1938 (very rare 1939) ... and in any case nickel is magnetic.
https://en.numista.com/forum/topic32893.html

Magnetic! Of course! How did I forget to try that?!
Thank you!

(edited to add: I had no idea of the rarity of one or the other until I looked at the older forum link. I was actually hoping I had the common aluminum bronze one because I already had a common year of the nickel version, so I'm happy with my cheap coin. I have one of each now!)