Hi Si.
I am looking to replace the viper on my .308 M67 (previoulsy my F/TR rig until I got the Sightron LRTD topped Dolphin).
The viper is fine, but the only reason for the cull is the turrets (and the finer AMD Ret, I am an AMD fan as it goes).
Being used to dialling in ranges, the viper turrets are a pain if you lose your place.
Incidentally, I got round the vernier marking issue on the Sightron by covering the 2 vertical sets of values either side of the vernier lines with some bright, fine graphics film.
I then just re marked the stadia 1-7 and replaced the turret...ideal.