Very unusual penny 1857 wrong weight size and thickness. Is it a genuine piece

hi everyone.

I recently agreed this piece and it has me intrigued. It looks genuine thanks to the detail on it but is is not the right weight size or thickness for a penny issued in 1857. However it does it weigh very similar to a post 1860 bun head penny as opposed to a young head victory penny. As you can see in the scans

Is it a genuine penny or a elaborate counterfeit

Weight is 9.14 grams and 30 mm diameter

Thank yoou for any help or guidance 

 In 1857 and before, there was no denomination. 

So the 1 Penny looked like others - and yours is the ½ Penny. 

N#12806 [9.45 g / 28.4 mm] 

 Determined by the : after REG at the top. The Penny does not have it. 

[Half / One] 

 Also - here on your coin - 

 The helmet plumes are shorter 

The exergue line on left is shorter 

So those plus the colon, all make it the same as the halfpenny.