Thread: Zero MOA rail/base - why?

It's best if possible to be near the scopes optical centre at the most common long range to be shot.
Also barrel indexing in a factory rifle is a lottery. It could end up at 6 o'clock ish which would mean some available elevation is lost.
And don't expect factory barrels to be perfectly straight in profile or bore centre to outer. Nor some custom barrels.
At least with a custom barrel fit it can be indexed to 12 o'clock which will aid elevation and give a best harmonics outcome.