When talking about zero shift, we
are going to address what is happening mechanically when the mount is removed
and reinstalled. It doesn’t take much for a zero to change due to the many
factors involved. The goal is to have as little movement as possible each time
it is taken on and off. Not all mounts are created equal, and some will perform
better by way of their design and construction. A lot of manufacturers get away
with stellar return to zero claims because their products aren’t properly
tested by end users that “set and forget” their optics. If a return to zero
mount is required, then our mount has no equal.
So, what makes the system work? Our
mounts were invented when I realized that obtaining a quick detach mount that
would truly return to zero was an issue. A mount was needed that could grab a
rail with exact, repeatable force every time it was installed. I figured a
spring, or a series of springs, could be used for this task (much like the
valve springs in an automobile). These springs withstand tens of thousands of
cycles under demanding conditions in a manner that is remarkable. If the
engineering criteria could be met, getting consistent results wouldn’t be a
problem.
Even though there are strict
specifications for rail dimensions, they always vary, so the mount design
needed to account for this. A small difference from rail to rail can cause
large shifts when attempting to design something repeatable that works in real
world conditions. By designing a “driver” that rides in a channel and uses a
series of powerful springs, we were able to account for differing dimensions.
The initial prototype worked, and the concept was sound, but getting
reliability and consistent performance was going to take some effort. This is
where the real work began.
With a linear driver, the mount is
simultaneously pulled across the rail and downwards. It grabs and engages the
rail in every direction. The springs ensure that the pressure exerted is
consistent every time. Return to zero comes down to one thing:
repeatability. Springs have what is
called a rate, meaning that they will have a certain amount of pressure for a
given distance of deflection, and in our case, travel. This is calculated by
how much the springs compress when installed on a rail. Since there is a
specification for a rail, we can accurately predict how much force is being
exerted when the mount is installed. The biggest benefit of using springs is
that this pressure repeats itself every time. The concept is very simple, but
not easy to execute.
The mount grabs with the
appropriate amount of force automatically - no adjustment on the user’s part is
required (this is where the auto compensation part of the BLAC name is
derived). Once the scope is zeroed, it can be taken on and off without limit. Every
time it is reinstalled, it will locate itself and grab with the exact same
force as the day it was made. This mechanical repeatability eliminates nearly
all variables that contribute to poor return to zero. As long as the mount is
reinstalled in the same location as before, no perceptible zero shift will
appear. This is return to zero technology at its finest.