5 Kurush Ottoman coin

I got this coin as a bargain for €1 from a mixed coin tray and it seems to be a 5 Kurush coin. (Mahmud II - 1808-39AD)

The date seems to be 1223 AH (1808), but it's not very clear what's the year of the reign.

I see in the Standard Catalog of Coins some coins bearing this value:

• KM# 564 0.7300 Silver Weight varies: 24.00-26.00 grams.
  
• KM# 591 0.2200 Silver Weight varies: 15.00-16.00 grams
  
• KM# 599 0.1700 Silver Weight varies: 13.00-16.00 grams
  

Inflation done the old fashioned way, not through banknotes. :)

Anyway, this coin is rather small (smaller than an American quarter or 0.20€ and much thinner), it's not even 10 grams and the metal appears to have much more copper than silver.

Regnal year is 78 which is very weird.

Yes, that's weird. It definitely looks like a 7, but I was thinking it might be a badly drawn 2.

In the catalog, there's no 5 kurush coin for regnal year 28.

We'll need to know more precise weight and diameter to determine the denomination.
It is obviously not 5 Kurush. Probably this is 20 Para from Mahmud II reign year AH1223//28 (about 1836 AD) mint in Constantinia (now Istanbul).

I think if I had this coin I would call it a 20 Para from 1834 28th year of the reign if I can count

If you look under the Wreath it clearly has a dot which means it is a Ninth issue coin

The 5 Kursh coin is 39 mm in this issue where as the 20 Para is 20 mm which is as you described it
just smaller than an American Quarter about 24.2 mm

The designs are very similar but if you look in the catalog the picture for the reignal year is very similar to yours as well and while I would say it looks like a 78 to me he only reigned for 30 some years

Also if you look on the 5 Kursh coin the wreath design at the bottom is a little different

 https://en.numista.com/catalogue/pieces20108.html

Anyway just me trying to confuse the issue even more

Your post came just a minute after mine, which means we were typing almost simultaneously and separately came to the same conclusion: 20 Para.

Just for info: there are many fakes with 78 at regnal year.

It's not a valuable coin, so I guess that if it's a fake, it might be an Ottoman-era fake?