From: firstname.lastname@example.org (Bartbob)
Subject: Re: Scope Quality Questions
Date: 8 Jun 1997 21:52:59 -0400
Although a huge number of folks want variable power scopes on their
accurate rifles, variables are not the most accurate scope made. Their
internal zoom lens' assembly is prone to not focussing the target image
repeatably on the reticule. Having measured several zoom scopes for this
repeatability, they can have up to 1 MOA or more error. Any error in this
area increases the group size one shoots by an amount equal to the error.
Leupold VariX III scopes are better than their VariX II scopes, but still
have a bit of non-repeatability; like up to 1/4th MOA. And the B&L Elite
variables are also among the best, but they also can have some error.
Redfields and Bushnell variables can have as much as 2 MOA of error. The
two Burris scopes I checked had some error on the bench collimator I used,
but I don't remember what it was.
Shooting groups is a very poor way of trying to measure a scope's
repeatability. You don't know what percent of the group's size is due to
the rifle plus ammo plus shooter variables and what percent is due to the
scope's variables. Using a proper collimator is the best way; there's no
variables from the rifle, ammo or shooter to cloud the data.
One can check their rifle's variable-power scope by first putting a
regular boresight collimator in the muzzle, then adjusting the W & E knobs
to make the scope's reticule intersect the collimator's reticule. Then
look through the scope and turn the zoom ring slowly from stop to stop.
Note how much the scope's reticule moves about the collimator's reticule.
Any error will be easily seen. Move the W & E knobs to realign the
reticules and you can find out what the error is in MOA. Note that when
the rifle's fired, recoil moves the zoom lens element's tubes a tiny bit
within the cam tube that holds them and they won't come to rest at exactly
the same place from shot to shot. You can also check the W & E adjustment
repeatability by moving one 5, 10 or 20 clicks off in one direction, then
reversing the direction and comming back the same amount. The reticules
should be back to perfect alignment.
If one wants to get the most accuracy from their rifle and ammunition, use
a fixed-power scope. Leupold's and Weaver's target models are probably
the best put together in the US.