Let the (not so good) pics do the talking:










With the original barrel; you would notice that the 308 barrel is actually 21", and hence, shorter.



And how it shoots? Below is with some mil surp ammo, iron sights, prone.
Shooter: A Friend (and a good shot)
Rifle: Brno ZKK600 (1970) 7x57 Rebarreled to 308
Ammunition: POF surplus
Distance: 100mtrs (110 yards)
Sights: Open sights
Shooting position: Prone, foreend 'pillow' rest.

Shooter: Myself
Rifle: Brno ZKK600 (1970) 7x57 Rebarreled to 308
Ammunition: POF surplus
Distance: 100mtrs(110 yards)
Sights: Open sights
Shooting position: Prone, foreend 'pillow' rest.

These were around 2.5" groups in prone position. I thought that was pretty good with the POF ammunition that generally hardly makes 1.5MOA with a scoped rifle.