What Cartridge is this?

[RL338]

My brother has a knack in picking up old obscured rifles. This time he acquired some ammo but no rifle , thank goodness. My question is does any keen eyes know what I have here?

A little help , here it is next to a 30-30.

 

[JD338]

What is the bullet diameter?

JD338

 

[RL338]

The bullet diameter would be a dead give away as it’s the only cartridge with it.
I should have stated I know it , just seeing if anyone could guess it.

 

[TexasLife]

30-40kreg

 

[TexasLife]

It's the only bottleneck rimmed cartridge I can think of besides the 7.62x54r

 

[RememberBaker]

.303 British?

 

[JD338]

8x57 JRS Mauser

JD338

 

[Hunter26]

8x50 Lebel or Mannlicher?

 

[filmjunkie4ever]

Looks like an 8x50 Lebel or 8x56 Hungarian to me.

 

[RL338]

8x56 Hungarian

Winner