King William IV Coin

I have a Copper 1834 King William IV coin,

I'm unsure of what denomination it is, 

I currently have it listed under Half penny, it's diameter is 24mm

N#12809 

A bit small though

This is the diameter of the coin

Maybe dipped in acid. 

Could be counterfeit or simply smaller because it's heavily circulated (or the catalog value is wrong, I haven't checked any reference). I did compare it with the example pictures and they looked very similar. On a second glance it seems the examples were cropped a bit to much if the remnants around the edge are an indicator of the true ends. So it could very well just be the wear and tear.