Subject: Re: Scope Quality Questions
From: Rock McMillan <email@example.com>
Date: Jun 17 1997
# 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.
The above statement is given as if there were only one type of optical
design being used in this country. It comes nearer to being right on
scopes with second focal plane reticles. On first focal plane reticled
scopes the light path passes the reticle at the focal plane of the
objective lens. From that point you could do anything you would like to
the light path and it would not change the point of impact. Scopes like
Ziess,SmitBender,McMillan VisionMaster and several others use the first
focal plane reticled scope design. It is much more difficult to make
scopes of this type so only the more expensive scopes use it with the
exception of a few Japanese scopes. I use the front focal plane reticle
so that I can remove the eyepiece and replace it with a light
intensifier tube on the second focal plane without change of point of
impact.( I can disclose this since it is a patented process.) The
reason some scopes change point of impact when the power is changed is
because the cross hair is not perfectly centered in the light path at
the second focal plane. This is an assembly problem. If pains are
taken in assembly it will not happen. One other point Weaver hasn't
been made in the US in about 9 years. For a look at my day& Night scope
look at www.mcmfamily.com