Here is a response I got from UltiMAK about some of the concerns expressed here.
First, we have tested this extensively, with massive amounts (in my
opinion) of ammunition-- far more than one would ever expend for any
useful purpose. We have fired over 700 rounds in a single afternoon,
using an Aimpoint Comp ML sight on a Mini-14, and over 1000 rounds using
an AK with the same model sight. Yes, the mount, and to a lesser
degree, the sight, will get hot under such conditions. This is also the
case with our AK mount, which has been on the market for three years.
So far, we have never experienced, nor have we been informed of, any
sight failure. The worst we have heard is that some people, who hold
the rifle in such a way as to touch the mount with the fingers while
shooting, have complained about discomfort after firing several dozen
rounds very quickly. For me, and for our other testers, it is a feat of
contortionism to hold a rifle in such a way, but everyone is built
If you have one of the few surviving automatics, and you are in the
habit of emptying several 30 round mags in a row without pause, this may
not be the system for you. However, if you are looking for a way to
improve the practical utility of your Mini-14, the M4-B is for you.
As for barrel problems, the mount will aid in cooling the barrel, due to
its direct contact, large surface area, and conductivity. Keep in mind
that adding mass, and therefore surface area, i.e. using a heavy barrel,
is the preferred method of dealing with the heat of increased firing
rates for light machineguns. The M4-B effectively adds mass, surface
area, and stiffness to the barrel. All reports we have received from
customers on the subject of accuracy, including our own experiences,
indicate the mount as improving accuracy.
Posted by the Reverend