Hello, it appeared to me that the model for the 5.56x45mm Nato rounds are bigger than it should be.
The 5.56 in game looks more like a 7.62 (case size) and weirdly is much larger than the 5.45x39 even though they're somewhat equal in irl. Also you could say the 5.45 in game is too thin in relation to the 7.62 even though they share almost the same case.
What's the issue?: i often in game confuse the 5.56x45 with the 7.62x39 and vice versa. And yea it is inauthenic.
Characteristics to consider:
7.62 -> chunky bullet and big "cone shape" case
5.45 -> almost the same case as 7.62 but long pointy bullet
5.56 -> slightly smaller, thin, straight case than 5.45 and short pointy bullet
Sadly i forgor to take a picture from ingame but you will see what i mean if you look it up for yourself.
And for comparison here's a pic from irl (7.62x39. 5.45x39 and 5.56x45)