UK 1740-1754 George II Half Penny

I have a UK 1740-1754 George II Half Penny, with the date worn.

The coin is worn, and only ‘17’ is visible. But "Georgius II Rex" and “Britannia” are clearly readable.

The unusual thing is that the diameter is 29 mm,  and the weight is 12.27 grams.

Are there any known varieties of this coin with a bigger diameter and a weight over 12 grams?

Thanks!

George III?  Pictures?

Please post some photos of your coin so that we can help, George II halfpennies have two different portraits one for the young king and one for the old king, by the dates you have given it would be the older portrait 

Thanks for the quick reply!

It's a George II coin, and it looks exactly like KM#579 (old bust). 

I've attached images.

I only posted this question because of the unusual size and weight.

Since the coin is very worn, the original diameter was probably 30mm or more, and the weight was obviously more.  

I've never seen anything like this. 

And yes, my scale is calibrated. I've checked it with a recent US nickel, which has exactly 5.00 grams. 

From my research it could well be an American forgery used in the thirteen states, they tended to be larger than the genuine coins 

Thanks!

Can you please point me to a link, article or catalogue reference about these American forgeries?